feat: proper exports implemented for C++ modules

src/core/CMakeLists.txt

@@ -46,6 +46,7 @@ add_mp_units_module(
             include/mp-units/bits/get_associated_quantity.h
             include/mp-units/bits/get_common_base.h
             include/mp-units/bits/magnitude.h
+            include/mp-units/bits/module_macros.h
             include/mp-units/bits/quantity_cast.h
             include/mp-units/bits/quantity_concepts.h
             include/mp-units/bits/quantity_point_concepts.h

src/core/include/mp-units/bits/dimension_concepts.h

@@ -24,11 +24,12 @@
 
 #include <mp-units/bits/expression_template.h>
 #include <mp-units/bits/external/type_traits.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/symbol_text.h>
 
 namespace mp_units {
 
-template<basic_symbol_text Symbol>
+MP_UNITS_EXPORT template<basic_symbol_text Symbol>
 struct base_dimension;
 
 namespace detail {
@@ -98,7 +99,7 @@ concept DerivedDimension = is_specialization_of<T, derived_dimension> || is_dime
  *
  * Satisfied by all dimension types for which either `BaseDimension<T>` or `DerivedDimension<T>` is `true`.
  */
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept Dimension = detail::BaseDimension<T> || detail::DerivedDimension<T>;
 
 /**
@@ -106,7 +107,7 @@ concept Dimension = detail::BaseDimension<T> || detail::DerivedDimension<T>;
  *
  * Satisfied when both argument satisfy a `Dimension` concept and when they compare equal.
  */
-template<typename T, auto D>
+MP_UNITS_EXPORT template<typename T, auto D>
 concept DimensionOf = Dimension<T> && Dimension<std::remove_const_t<decltype(D)>> && (T{} == D);
 
 }  // namespace mp_units

src/core/include/mp-units/bits/external/algorithm.h

@@ -23,10 +23,13 @@
 #pragma once
 
 #include <mp-units/bits/external/hacks.h>  // IWYU pragma: keep
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <compare>
 #include <initializer_list>
 #include <iterator>
 #include <ranges>
+#endif
 
 namespace mp_units::detail {
 

src/core/include/mp-units/bits/external/fixed_string.h

@@ -24,17 +24,17 @@
 
 // TODO use <algorithm> when moved to C++20 modules (parsing takes too long for each translation unit)
 #include <mp-units/bits/external/algorithm.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/compat_macros.h>  // IWYU pragma: keep
 
-// IWYU pragma: begin_exports
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <compare>
+#include <cstddef>
 #include <cstdlib>
 #include <ostream>
-// IWYU pragma: end_exports
-
-#include <cstddef>
-
+#endif
 
+MP_UNITS_EXPORT
 namespace mp_units {
 
 /**

src/core/include/mp-units/bits/external/hacks.h

@@ -22,7 +22,9 @@
 
 #pragma once
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <version>
+#endif
 
 #if __clang__
 #define MP_UNITS_COMP_CLANG __clang_major__

src/core/include/mp-units/bits/external/math_concepts.h

@@ -22,7 +22,9 @@
 
 #pragma once
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cstdint>
+#endif
 
 namespace mp_units::detail {
 

src/core/include/mp-units/bits/external/prime.h

@@ -23,12 +23,15 @@
 #pragma once
 
 #include <mp-units/bits/external/algorithm.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <array>
 #include <cstddef>
 #include <cstdint>
 #include <numeric>
 #include <optional>
 #include <tuple>
+#endif
 
 namespace mp_units::detail {
 

src/core/include/mp-units/bits/external/type_list.h

@@ -23,9 +23,12 @@
 #pragma once
 
 #include <mp-units/bits/external/hacks.h>  // IWYU pragma: keep
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cstddef>
 #include <type_traits>
 #include <utility>
+#endif
 
 MP_UNITS_DIAGNOSTIC_PUSH
 MP_UNITS_DIAGNOSTIC_IGNORE_EXPR_ALWAYS_TF

src/core/include/mp-units/bits/external/type_name.h

@@ -2,7 +2,9 @@
 
 #pragma once
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <string_view>
+#endif
 
 template<typename T>
 [[nodiscard]] consteval std::string_view type_name()

src/core/include/mp-units/bits/external/type_traits.h

@@ -23,8 +23,12 @@
 #pragma once
 
 #include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/module_macros.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <type_traits>
 #include <utility>
+#endif
 
 namespace mp_units {
 
@@ -45,6 +49,8 @@ struct conditional_impl<true> {
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 template<bool B, typename T, typename F>
 using conditional = MP_UNITS_TYPENAME detail::conditional_impl<B>::template type<T, F>;
 
@@ -71,6 +77,8 @@ inline constexpr bool is_specialization_of_v = false;
 template<auto... Params, template<auto...> typename Type>
 inline constexpr bool is_specialization_of_v<Type<Params...>, Type> = true;
 
+MP_UNITS_EXPORT_END
+
 // is_derived_from_specialization_of
 namespace detail {
 

src/core/include/mp-units/bits/fmt.h

@@ -29,11 +29,14 @@
 
 #pragma once
 
-#include <gsl/gsl-lite.hpp>
 #include <mp-units/compat_macros.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <gsl/gsl-lite.hpp>
 #include <concepts>
 #include <limits>
 #include <string_view>
+#endif
 
 // most of the below code is based on/copied from fmtlib
 

src/core/include/mp-units/bits/magnitude.h

@@ -28,14 +28,18 @@
 #include <mp-units/bits/external/prime.h>
 #include <mp-units/bits/external/type_name.h>
 #include <mp-units/bits/external/type_traits.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/ratio.h>
 #include <mp-units/bits/symbol_text.h>
 #include <mp-units/bits/text_tools.h>
 #include <mp-units/customization_points.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <concepts>
 #include <cstdint>
 #include <numbers>
 #include <optional>
+#endif
 
 namespace mp_units {
 
@@ -59,7 +63,7 @@ inline constexpr bool is_specialization_of_magnitude = false;
 /**
  * @brief  Concept to detect whether T is a valid Magnitude.
  */
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept Magnitude = detail::is_magnitude<T>;
 
 /**
@@ -525,6 +529,8 @@ constexpr T get_value(const magnitude<Ms...>&)
   return result;
 }
 
+MP_UNITS_EXPORT_BEGIN
+
 /**
  * @brief  A convenient Magnitude constant for pi, which we can manipulate like a regular number.
  */
@@ -575,6 +581,8 @@ template<auto... Ms>
   return pow<1, 3>(m);
 }
 
+MP_UNITS_EXPORT_END
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 // Magnitude product implementation.
 
@@ -595,6 +603,7 @@ consteval bool less(MagnitudeSpec auto lhs, MagnitudeSpec auto rhs)
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
 
 // Base cases, for when either (or both) inputs are the identity.
 constexpr Magnitude auto operator*(magnitude<>, magnitude<>) { return magnitude<>{}; }
@@ -644,6 +653,8 @@ template<auto H1, auto... T1, auto H2, auto... T2>
 
 [[nodiscard]] consteval auto operator/(Magnitude auto l, Magnitude auto r) { return l * pow<-1>(r); }
 
+MP_UNITS_EXPORT_END
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 // Magnitude numerator and denominator implementation.
 
@@ -776,7 +787,7 @@ using common_magnitude_type = decltype(common_magnitude_type_impl(M));
 // To provide the first factor for a given number, specialize this variable template.
 //
 // WARNING:  The program behaviour will be undefined if you provide a wrong answer, so check your math!
-template<std::intmax_t N>
+MP_UNITS_EXPORT template<std::intmax_t N>
 inline constexpr std::optional<std::intmax_t> known_first_factor = std::nullopt;
 
 namespace detail {
@@ -819,14 +830,14 @@ inline constexpr auto prime_factorization_v = prime_factorization<N>::value;
  * This will be the main way end users create Magnitudes.  They should rarely (if ever) create a magnitude<...> by
  * manually adding base powers.
  */
-template<ratio R>
+MP_UNITS_EXPORT template<ratio R>
   requires detail::gt_zero<R.num>
 inline constexpr Magnitude auto mag = detail::prime_factorization_v<R.num> / detail::prime_factorization_v<R.den>;
 
 /**
  * @brief  Create a Magnitude which is some rational number raised to a rational power.
  */
-template<ratio Base, ratio Pow>
+MP_UNITS_EXPORT template<ratio Base, ratio Pow>
   requires detail::gt_zero<Base.num>
 inline constexpr Magnitude auto mag_power = pow<Pow.num, Pow.den>(mag<Base>);
 

src/core/include/mp-units/bits/module_macros.h

@@ -0,0 +1,40 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// the below line is commented out on purpose (clang-17 does not work otherwise)
+// #pragma once
+
+#ifdef MP_UNITS_IN_MODULE_INTERFACE
+
+#define MP_UNITS_EXPORT export
+#define MP_UNITS_EXPORT_BEGIN \
+  export                      \
+  {
+#define MP_UNITS_EXPORT_END }
+
+#else
+
+#define MP_UNITS_EXPORT
+#define MP_UNITS_EXPORT_BEGIN
+#define MP_UNITS_EXPORT_END
+
+#endif

src/core/include/mp-units/bits/quantity_cast.h

@@ -22,11 +22,16 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_concepts.h>
 #include <mp-units/bits/quantity_point_concepts.h>
 #include <mp-units/reference.h>
-#include <type_traits>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <type_traits>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units {
 
 /**

src/core/include/mp-units/bits/quantity_concepts.h

@@ -22,6 +22,7 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_spec_concepts.h>
 #include <mp-units/bits/reference_concepts.h>
 #include <mp-units/bits/representation_concepts.h>
@@ -29,7 +30,7 @@
 
 namespace mp_units {
 
-template<Reference auto R, RepresentationOf<get_quantity_spec(R).character> Rep>
+MP_UNITS_EXPORT template<Reference auto R, RepresentationOf<get_quantity_spec(R).character> Rep>
 class quantity;
 
 namespace detail {
@@ -43,6 +44,8 @@ inline constexpr bool is_derived_from_specialization_of_quantity =
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 /**
  * @brief A concept matching all quantities in the library
  *
@@ -82,4 +85,6 @@ concept QuantityLike = requires {
   } -> detail::ConversionSpecOf<T>;
 };
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units

src/core/include/mp-units/bits/quantity_point_concepts.h

@@ -22,6 +22,7 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_concepts.h>
 #include <mp-units/bits/quantity_spec_concepts.h>
 #include <mp-units/bits/reference_concepts.h>
@@ -30,7 +31,7 @@
 
 namespace mp_units {
 
-template<typename Derived, QuantitySpec auto QS>
+MP_UNITS_EXPORT template<typename Derived, QuantitySpec auto QS>
 struct absolute_point_origin;
 
 namespace detail {
@@ -62,10 +63,10 @@ concept AbsolutePointOrigin =
  *
  * Satisfied by all types being either a specialization or derived from `quantity_point`
  */
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept QuantityPoint = detail::is_quantity_point<T>;
 
-template<QuantityPoint auto QP>
+MP_UNITS_EXPORT template<QuantityPoint auto QP>
 struct relative_point_origin;
 
 namespace detail {
@@ -94,7 +95,7 @@ concept RelativePointOrigin =
  *
  * Satisfied by either quantity points or by all types derived from `absolute_point_origin` class template.
  */
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept PointOrigin = detail::AbsolutePointOrigin<T> || detail::RelativePointOrigin<T>;
 
 /**
@@ -102,11 +103,11 @@ concept PointOrigin = detail::AbsolutePointOrigin<T> || detail::RelativePointOri
  *
  * Satisfied by all quantity point origins that are defined using a provided quantity specification.
  */
-template<typename T, auto QS>
+MP_UNITS_EXPORT template<typename T, auto QS>
 concept PointOriginFor = PointOrigin<T> && QuantitySpecOf<std::remove_const_t<decltype(QS)>, T::quantity_spec>;
 
-template<Reference auto R, PointOriginFor<get_quantity_spec(R)> auto PO,
-         RepresentationOf<get_quantity_spec(R).character> Rep>
+MP_UNITS_EXPORT template<Reference auto R, PointOriginFor<get_quantity_spec(R)> auto PO,
+                         RepresentationOf<get_quantity_spec(R).character> Rep>
 class quantity_point;
 
 namespace detail {
@@ -151,7 +152,7 @@ concept SameAbsolutePointOriginAs =
  * the provided quantity_spec type, or quantity points having the origin with the same
  * `absolute_point_origin`.
  */
-template<typename QP, auto V>
+MP_UNITS_EXPORT template<typename QP, auto V>
 concept QuantityPointOf =
   QuantityPoint<QP> && (QuantitySpecOf<std::remove_const_t<decltype(QP::quantity_spec)>, V> ||
                         detail::SameAbsolutePointOriginAs<std::remove_const_t<decltype(QP::absolute_point_origin)>, V>);
@@ -162,7 +163,7 @@ concept QuantityPointOf =
  * Satisfied by all external types (not-defined in mp-units) that via a `quantity_point_like_traits` provide
  * all quantity_point-specific information.
  */
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept QuantityPointLike = requires {
   quantity_point_like_traits<T>::reference;
   requires Reference<std::remove_const_t<decltype(quantity_point_like_traits<T>::reference)>>;

src/core/include/mp-units/bits/quantity_spec_concepts.h

@@ -24,9 +24,11 @@
 
 #include <mp-units/bits/dimension_concepts.h>
 #include <mp-units/bits/expression_template.h>
+#include <mp-units/bits/module_macros.h>
 
 namespace mp_units {
 
+MP_UNITS_EXPORT
 #ifdef __cpp_explicit_this_parameter
 template<auto...>
 #else
@@ -125,11 +127,11 @@ concept IntermediateDerivedQuantitySpec =
 }  // namespace detail
 
 
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept QuantitySpec =
   detail::NamedQuantitySpec<T> || detail::IntermediateDerivedQuantitySpec<T> || detail::QuantityKindSpec<T>;
 
-template<QuantitySpec Q>
+MP_UNITS_EXPORT template<QuantitySpec Q>
 [[nodiscard]] consteval detail::QuantityKindSpec auto get_kind(Q q);
 
 namespace detail {
@@ -142,7 +144,7 @@ concept NestedQuantityKindSpecOf =
 
 }
 
-template<typename T, auto QS>
+MP_UNITS_EXPORT template<typename T, auto QS>
 concept QuantitySpecOf =
   QuantitySpec<T> && QuantitySpec<std::remove_const_t<decltype(QS)>> && implicitly_convertible(T{}, QS) &&
   // the below is to make the following work

src/core/include/mp-units/bits/ratio.h

@@ -24,9 +24,13 @@
 
 #include <gsl/gsl-lite.hpp>
 #include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/module_macros.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <compare>
 #include <cstdint>
 #include <numeric>
+#endif
 
 namespace mp_units {
 
@@ -63,7 +67,7 @@ template<typename T>
  * This class is really similar to @c std::ratio.  An important difference is the fact that the objects of that class
  * are used as class NTTPs rather then a type template parameter kind.
  */
-struct ratio {
+MP_UNITS_EXPORT struct ratio {
   std::intmax_t num;
   std::intmax_t den;
 

src/core/include/mp-units/bits/reference_concepts.h

@@ -22,12 +22,13 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_spec_concepts.h>
 #include <mp-units/bits/unit_concepts.h>
 
 namespace mp_units {
 
-template<QuantitySpec Q, Unit U>
+MP_UNITS_EXPORT template<QuantitySpec Q, Unit U>
 struct reference;
 
 namespace detail {
@@ -41,6 +42,8 @@ struct is_specialization_of_reference<reference<Q, U>> : std::true_type {};
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 /**
  * @brief A concept matching all references in the library.
  *
@@ -74,4 +77,6 @@ template<typename Q, typename U>
 template<typename T, auto QS>
 concept ReferenceOf = Reference<T> && QuantitySpecOf<std::remove_const_t<decltype(get_quantity_spec(T{}))>, QS>;
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units

src/core/include/mp-units/bits/representation_concepts.h

@@ -22,11 +22,15 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/customization_points.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <concepts>
 #include <cstdint>
 #include <functional>
 #include <type_traits>
+#endif
 
 namespace mp_units {
 
@@ -48,7 +52,7 @@ namespace mp_units {
  * For example, the Cauchy stress tensor possess magnitude, direction,
  * and orientation qualities.
  */
-enum class quantity_character { scalar, vector, tensor };
+MP_UNITS_EXPORT enum class quantity_character { scalar, vector, tensor };
 
 namespace detail {
 
@@ -75,10 +79,10 @@ concept Scalable =
 
 }  // namespace detail
 
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept Representation = (is_scalar<T> || is_vector<T> || is_tensor<T>)&&std::regular<T> && detail::Scalable<T>;
 
-template<typename T, quantity_character Ch>
+MP_UNITS_EXPORT template<typename T, quantity_character Ch>
 concept RepresentationOf = Representation<T> && ((Ch == quantity_character::scalar && is_scalar<T>) ||
                                                  (Ch == quantity_character::vector && is_vector<T>) ||
                                                  (Ch == quantity_character::tensor && is_tensor<T>));

src/core/include/mp-units/bits/symbol_text.h

@@ -25,15 +25,19 @@
 // IWYU pragma: begin_exports
 #include <mp-units/bits/external/fixed_string.h>
 #include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/module_macros.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <gsl/gsl-lite.hpp>
 #include <compare>
 #include <cstddef>
 #include <cstdint>
-// IWYU pragma: end_exports
-
-#include <gsl/gsl-lite.hpp>
+#endif
 
 #if __cpp_lib_text_encoding
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <text_encoding>
+#endif
 static_assert(std::text_encoding::literal().mib() == std::text_encoding::id::UTF8);
 #endif
 
@@ -74,7 +78,7 @@ constexpr fixed_u8string<N> to_u8string(fixed_string<N> txt)
  * @tparam N The size of a Unicode symbol
  * @tparam M The size of the ASCII-only symbol
  */
-template<std::size_t N, std::size_t M>
+MP_UNITS_EXPORT template<std::size_t N, std::size_t M>
 struct basic_symbol_text {
   fixed_u8string<N> unicode_;
   fixed_string<M> ascii_;

src/core/include/mp-units/bits/unit_concepts.h

@@ -24,6 +24,7 @@
 
 #include <mp-units/bits/expression_template.h>
 #include <mp-units/bits/magnitude.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_spec_concepts.h>
 #include <mp-units/bits/symbol_text.h>
 
@@ -42,13 +43,13 @@ struct is_unit : std::false_type {};
  *
  * Satisfied by all unit types provided by the library.
  */
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept Unit = detail::is_unit<T>::value;
 
 template<Magnitude auto M, Unit U>
 struct scaled_unit;
 
-template<basic_symbol_text Symbol, auto...>
+MP_UNITS_EXPORT template<basic_symbol_text Symbol, auto...>
 struct named_unit;
 
 namespace detail {
@@ -84,13 +85,13 @@ concept NamedUnit =
  * `hour` or `degree_Celsius`. For those a partial specialization with the value `false` should be
  * provided.
  */
-template<Unit auto V>
+MP_UNITS_EXPORT template<Unit auto V>
 inline constexpr bool unit_can_be_prefixed = true;
 
 /**
  * @brief A concept to be used to define prefixes for a unit
  */
-template<typename T>
+MP_UNITS_EXPORT template<typename T>
 concept PrefixableUnit = detail::NamedUnit<T> && unit_can_be_prefixed<T{}>;
 
 namespace detail {
@@ -113,7 +114,7 @@ concept DerivedUnitExpr = Unit<T> || detail::is_power_of_unit<T> || detail::is_p
 template<detail::DerivedUnitExpr... Expr>
 struct derived_unit;
 
-template<basic_symbol_text Symbol, Magnitude auto M, PrefixableUnit auto U>
+MP_UNITS_EXPORT template<basic_symbol_text Symbol, Magnitude auto M, PrefixableUnit auto U>
   requires(!Symbol.empty())
 struct prefixed_unit;
 
@@ -177,7 +178,7 @@ template<Unit U>
 /**
  * @brief A concept matching all units that can be used as quantity references
  */
-template<typename U>
+MP_UNITS_EXPORT template<typename U>
 concept AssociatedUnit = Unit<U> && detail::has_associated_quantity(U{});
 
 /**
@@ -186,7 +187,7 @@ concept AssociatedUnit = Unit<U> && detail::has_associated_quantity(U{});
  * Satisfied by all units associated with the quantity_spec being the instantiation derived from
  * the provided quantity_spec type.
  */
-template<typename U, auto QS>
+MP_UNITS_EXPORT template<typename U, auto QS>
 concept UnitOf =
   AssociatedUnit<U> && QuantitySpec<std::remove_const_t<decltype(QS)>> &&
   implicitly_convertible(get_quantity_spec(U{}), QS) &&
@@ -205,7 +206,7 @@ namespace detail {
  * Satisfied by all units that have the same canonical reference as `U2` and in case they
  * have associated quantity specification it should satisfy `UnitOf<QS>`.
  */
-template<typename U, auto U2, auto QS>
+MP_UNITS_EXPORT template<typename U, auto U2, auto QS>
 concept UnitCompatibleWith =
   Unit<U> && Unit<std::remove_const_t<decltype(U2)>> && QuantitySpec<std::remove_const_t<decltype(QS)>> &&
   (!AssociatedUnit<U> || UnitOf<U, QS>)&&detail::have_same_canonical_reference_unit(U{}, U2);

src/core/include/mp-units/bits/value_cast.h

@@ -22,6 +22,7 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_concepts.h>
 #include <mp-units/bits/quantity_point_concepts.h>
 #include <mp-units/bits/representation_concepts.h>
@@ -29,6 +30,7 @@
 #include <mp-units/bits/unit_concepts.h>
 #include <mp-units/reference.h>
 
+MP_UNITS_EXPORT
 namespace mp_units {
 
 /**

src/core/include/mp-units/compare.h

@@ -22,8 +22,13 @@
 
 #pragma once
 
-#include <compare>
+#include <mp-units/bits/module_macros.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <compare>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units {
 
 template<typename T>

src/core/include/mp-units/customization_points.h

@@ -23,11 +23,17 @@
 #pragma once
 
 #include <mp-units/bits/external/type_traits.h>
+#include <mp-units/bits/module_macros.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <limits>
 #include <type_traits>
+#endif
 
 namespace mp_units {
 
+MP_UNITS_EXPORT_BEGIN
+
 /**
  * @brief Specifies if a value of a type should be treated as a floating-point value
  *
@@ -149,15 +155,6 @@ struct convert_implicitly {
   }
 };
 
-namespace detail {
-
-template<typename T>
-concept ConversionSpec = is_specialization_of<T, convert_explicitly> || is_specialization_of<T, convert_implicitly>;
-
-template<typename T, typename U>
-concept ConversionSpecOf = ConversionSpec<T> && std::same_as<typename T::value_type, U>;
-
-}  // namespace detail
 
 /**
  * @brief Provides support for external quantity-like types
@@ -192,4 +189,16 @@ struct quantity_like_traits;
 template<typename T>
 struct quantity_point_like_traits;
 
+MP_UNITS_EXPORT_END
+
+namespace detail {
+
+template<typename T>
+concept ConversionSpec = is_specialization_of<T, convert_explicitly> || is_specialization_of<T, convert_implicitly>;
+
+template<typename T, typename U>
+concept ConversionSpecOf = ConversionSpec<T> && std::same_as<typename T::value_type, U>;
+
+}  // namespace detail
+
 }  // namespace mp_units

src/core/include/mp-units/dimension.h

@@ -25,6 +25,7 @@
 #include <mp-units/bits/dimension_concepts.h>
 #include <mp-units/bits/expression_template.h>
 #include <mp-units/bits/external/type_traits.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/symbol_text.h>
 
 namespace mp_units {
@@ -57,7 +58,7 @@ namespace mp_units {
  *
  * @tparam Symbol an unique identifier of the base dimension used to provide dimensional analysis support
  */
-template<basic_symbol_text Symbol>
+MP_UNITS_EXPORT template<basic_symbol_text Symbol>
 struct base_dimension {
   static constexpr auto symbol = Symbol;  ///< Unique base dimension identifier
 };
@@ -124,7 +125,7 @@ struct derived_dimension : detail::expr_fractions<detail::is_dimension_one, Expr
  * dimensions are zero. It is a dimension of a quantity of dimension one also known as
  * "dimensionless".
  */
-inline constexpr struct dimension_one : derived_dimension<> {
+MP_UNITS_EXPORT inline constexpr struct dimension_one : derived_dimension<> {
 } dimension_one;
 
 namespace detail {
@@ -136,14 +137,14 @@ struct is_dimension_one<struct dimension_one> : std::true_type {};
 
 // Operators
 
-template<Dimension Lhs, Dimension Rhs>
+MP_UNITS_EXPORT template<Dimension Lhs, Dimension Rhs>
 [[nodiscard]] consteval Dimension auto operator*(Lhs, Rhs)
 {
   return detail::expr_multiply<derived_dimension, struct dimension_one, detail::type_list_of_base_dimension_less>(
     Lhs{}, Rhs{});
 }
 
-template<Dimension Lhs, Dimension Rhs>
+MP_UNITS_EXPORT template<Dimension Lhs, Dimension Rhs>
 [[nodiscard]] consteval Dimension auto operator/(Lhs, Rhs)
 {
   return detail::expr_divide<derived_dimension, struct dimension_one, detail::type_list_of_base_dimension_less>(Lhs{},
@@ -163,13 +164,13 @@ template<auto Symbol>
 
 }  // namespace detail
 
-template<Dimension Lhs, Dimension Rhs>
+MP_UNITS_EXPORT template<Dimension Lhs, Dimension Rhs>
 [[nodiscard]] consteval bool operator==(Lhs lhs, Rhs rhs)
 {
   return is_same_v<Lhs, Rhs> || detail::derived_from_the_same_base_dimension(lhs, rhs);
 }
 
-[[nodiscard]] consteval Dimension auto inverse(Dimension auto d) { return dimension_one / d; }
+MP_UNITS_EXPORT [[nodiscard]] consteval Dimension auto inverse(Dimension auto d) { return dimension_one / d; }
 
 /**
  * @brief Computes the value of a dimension raised to the `Num/Den` power
@@ -180,7 +181,7 @@ template<Dimension Lhs, Dimension Rhs>
  *
  * @return Dimension The result of computation
  */
-template<std::intmax_t Num, std::intmax_t Den = 1, Dimension D>
+MP_UNITS_EXPORT template<std::intmax_t Num, std::intmax_t Den = 1, Dimension D>
   requires detail::non_zero<Den>
 [[nodiscard]] consteval Dimension auto pow(D d)
 {
@@ -201,7 +202,7 @@ template<std::intmax_t Num, std::intmax_t Den = 1, Dimension D>
  *
  * @return Dimension The result of computation
  */
-[[nodiscard]] consteval Dimension auto sqrt(Dimension auto d) { return pow<1, 2>(d); }
+MP_UNITS_EXPORT [[nodiscard]] consteval Dimension auto sqrt(Dimension auto d) { return pow<1, 2>(d); }
 
 /**
  * @brief Computes the cubic root of a dimension
@@ -210,7 +211,7 @@ template<std::intmax_t Num, std::intmax_t Den = 1, Dimension D>
  *
  * @return Dimension The result of computation
  */
-[[nodiscard]] consteval Dimension auto cbrt(Dimension auto d) { return pow<1, 3>(d); }
+MP_UNITS_EXPORT [[nodiscard]] consteval Dimension auto cbrt(Dimension auto d) { return pow<1, 3>(d); }
 
 
 // TODO consider adding the support for text output of the dimensional equation

src/core/include/mp-units/format.h

@@ -28,8 +28,10 @@
 #include <mp-units/customization_points.h>
 #include <mp-units/quantity.h>
 #include <mp-units/unit.h>
-#include <cstdint>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <cstdint>
+#endif
 
 namespace mp_units::detail {
 

src/core/include/mp-units/math.h

@@ -22,20 +22,20 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/value_cast.h>
 #include <mp-units/customization_points.h>
 #include <mp-units/quantity.h>
 #include <mp-units/unit.h>
 
-// IWYU pragma: begin_exports
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cmath>
 #include <cstdint>
-// IWYU pragma: end_exports
-
 #include <limits>
+#endif
 
+MP_UNITS_EXPORT
 namespace mp_units {
-
 /**
  * @brief Computes the value of a quantity raised to the `Num/Den` power
  *

src/core/include/mp-units/ostream.h

@@ -23,9 +23,13 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/quantity.h>
 #include <mp-units/unit.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <sstream>
+#endif
 
 namespace mp_units {
 
@@ -51,6 +55,8 @@ void to_stream(std::basic_ostream<CharT, Traits>& os, const quantity<R, Rep>& q)
 
 }  //  namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 template<typename CharT, typename Traits, Unit U>
 std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, U u)
 {
@@ -86,4 +92,6 @@ std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>&
   return os;
 }
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units

src/core/include/mp-units/quantity.h

@@ -24,6 +24,7 @@
 #pragma once
 
 #include <mp-units/bits/dimension_concepts.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_concepts.h>
 #include <mp-units/bits/quantity_spec_concepts.h>
 #include <mp-units/bits/reference_concepts.h>
@@ -32,8 +33,11 @@
 #include <mp-units/bits/unit_concepts.h>
 #include <mp-units/customization_points.h>
 #include <mp-units/reference.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <compare>
 #include <utility>
+#endif
 
 // the below is not used in this header but should be exposed with it
 #include <mp-units/bits/quantity_cast.h>
@@ -82,6 +86,8 @@ using common_quantity_for = quantity<common_reference(Q1::reference, Q2::referen
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 /**
  * @brief A quantity
  *
@@ -520,6 +526,8 @@ template<auto R1, typename Rep1, auto R2, typename Rep2>
   return ct_lhs.numerical_value_ref_in(ct::unit) <=> ct_rhs.numerical_value_ref_in(ct::unit);
 }
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units
 
 namespace std {

src/core/include/mp-units/quantity_point.h

@@ -22,21 +22,25 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_point_concepts.h>
 #include <mp-units/compare.h>
 #include <mp-units/customization_points.h>
 #include <mp-units/quantity.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <compare>
+#endif
 
 namespace mp_units {
 
-template<typename Derived, QuantitySpec auto QS>
+MP_UNITS_EXPORT template<typename Derived, QuantitySpec auto QS>
 struct absolute_point_origin {
   static constexpr QuantitySpec auto quantity_spec = QS;
   using _type_ = absolute_point_origin;
 };
 
-template<QuantityPoint auto QP>
+MP_UNITS_EXPORT template<QuantityPoint auto QP>
 struct relative_point_origin {
   static constexpr QuantityPoint auto quantity_point = QP;
   static constexpr QuantitySpec auto quantity_spec = []() {
@@ -52,7 +56,7 @@ struct relative_point_origin {
 template<QuantitySpec auto QS>
 struct zeroth_point_origin_ : absolute_point_origin<zeroth_point_origin_<QS>, QS> {};
 
-template<QuantitySpec auto QS>
+MP_UNITS_EXPORT template<QuantitySpec auto QS>
 inline constexpr zeroth_point_origin_<QS> zeroth_point_origin;
 
 namespace detail {
@@ -71,7 +75,7 @@ template<PointOrigin PO>
 
 }  // namespace detail
 
-template<PointOrigin PO1, PointOrigin PO2>
+MP_UNITS_EXPORT template<PointOrigin PO1, PointOrigin PO2>
 [[nodiscard]] consteval bool operator==(PO1 po1, PO2 po2)
 {
   if constexpr (detail::AbsolutePointOrigin<PO1> && detail::AbsolutePointOrigin<PO2>)
@@ -86,7 +90,7 @@ template<PointOrigin PO1, PointOrigin PO2>
     return detail::same_absolute_point_origins(po1, po2) && is_eq_zero(PO2::quantity_point.quantity_from_zero());
 }
 
-template<Reference R>
+MP_UNITS_EXPORT template<Reference R>
 [[nodiscard]] consteval PointOriginFor<get_quantity_spec(R{})> auto default_point_origin(R)
 {
   if constexpr (requires { get_unit(R{}).point_origin; })
@@ -108,6 +112,8 @@ template<PointOrigin PO>
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 /**
  * @brief A quantity point
  *
@@ -507,4 +513,6 @@ template<QuantityPoint QP1, QuantityPointOf<QP1::absolute_point_origin> QP2>
     return lhs - lhs.absolute_point_origin == rhs - rhs.absolute_point_origin;
 }
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units

src/core/include/mp-units/quantity_spec.h

@@ -27,19 +27,22 @@
 #include <mp-units/bits/external/type_name.h>
 #include <mp-units/bits/external/type_traits.h>
 #include <mp-units/bits/get_common_base.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_concepts.h>
 #include <mp-units/bits/quantity_spec_concepts.h>
 #include <mp-units/bits/reference_concepts.h>
 #include <mp-units/bits/representation_concepts.h>
 #include <mp-units/compat_macros.h>
 #include <mp-units/dimension.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <tuple>
+#endif
 
 namespace mp_units {
 
 namespace detail {
 
-
 template<QuantitySpec QS, Unit U>
   requires(!AssociatedUnit<U>) || UnitOf<U, QS{}>
 [[nodiscard]] consteval Reference auto make_reference(QS, U u)
@@ -143,6 +146,8 @@ struct quantity_spec_interface {
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 /**
  * @brief Quantity Specification
  *
@@ -171,6 +176,8 @@ struct quantity_spec;
 inline constexpr struct is_kind {
 } is_kind;
 
+MP_UNITS_EXPORT_END
+
 /**
  * @brief Specialization defining a base quantity
  *
@@ -432,7 +439,7 @@ struct derived_quantity_spec :
  * Quantity of dimension one also commonly named as "dimensionless" is a quantity with a dimension
  * for which all the exponents of the factors corresponding to the base dimensions are zero.
  */
-QUANTITY_SPEC(dimensionless, derived_quantity_spec<>{});
+MP_UNITS_EXPORT QUANTITY_SPEC(dimensionless, derived_quantity_spec<>{});
 
 /**
  * @brief Quantity kind specifier
@@ -469,7 +476,7 @@ struct kind_of_<Q> : quantity_spec<kind_of_<Q>, Q{}> {
 };
 #endif
 
-template<detail::QuantitySpecWithNoSpecifiers auto Q>
+MP_UNITS_EXPORT template<detail::QuantitySpecWithNoSpecifiers auto Q>
   requires(detail::get_kind_tree_root(Q) == Q)
 inline constexpr kind_of_<std::remove_const_t<decltype(Q)>> kind_of;
 
@@ -498,6 +505,8 @@ template<QuantitySpec Q>
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 // Operators
 
 template<QuantitySpec Lhs, QuantitySpec Rhs>
@@ -579,6 +588,7 @@ template<std::intmax_t Num, std::intmax_t Den = 1, QuantitySpec Q>
  */
 [[nodiscard]] consteval QuantitySpec auto cbrt(QuantitySpec auto q) { return pow<1, 3>(q); }
 
+MP_UNITS_EXPORT_END
 
 namespace detail {
 
@@ -1386,6 +1396,8 @@ template<QuantitySpec From, QuantitySpec To>
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 template<QuantitySpec From, QuantitySpec To>
 [[nodiscard]] consteval bool implicitly_convertible(From from, To to)
 {
@@ -1410,6 +1422,8 @@ template<QuantitySpec QS1, QuantitySpec QS2>
   return implicitly_convertible(qs1, qs2) && implicitly_convertible(qs2, qs1);
 }
 
+MP_UNITS_EXPORT_END
+
 namespace detail {
 
 template<QuantitySpec Q>
@@ -1454,6 +1468,8 @@ template<QuantitySpec Q>
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 template<QuantitySpec Q>
 [[nodiscard]] consteval detail::QuantityKindSpec auto get_kind(Q q)
 {
@@ -1502,4 +1518,6 @@ template<QuantitySpec Q1, QuantitySpec Q2>
   return common_quantity_spec(common_quantity_spec(q1, q2), q3, rest...);
 }
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units

src/core/include/mp-units/random.h

@@ -22,9 +22,13 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/quantity.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <functional>
 #include <random>
+#endif
 
 namespace mp_units {
 
@@ -82,6 +86,8 @@ std::vector<typename Q::rep> fw_bl_pwl(std::initializer_list<Q>& bl, UnaryOperat
 }
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 template<Quantity Q>
   requires std::integral<typename Q::rep>
 struct uniform_int_distribution : public std::uniform_int_distribution<typename Q::rep> {
@@ -571,4 +577,6 @@ public:
   Q max() const { return base::max() * Q::reference; }
 };
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units

src/core/include/mp-units/reference.h

@@ -23,6 +23,7 @@
 #pragma once
 
 #include <mp-units/bits/get_associated_quantity.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_concepts.h>
 #include <mp-units/bits/reference_concepts.h>
 #include <mp-units/bits/representation_concepts.h>
@@ -36,6 +37,8 @@ using reference_t = reference<std::remove_const_t<decltype(Q)>, std::remove_cons
 
 }
 
+MP_UNITS_EXPORT_BEGIN
+
 [[nodiscard]] consteval QuantitySpec auto get_quantity_spec(AssociatedUnit auto u)
 {
   return detail::get_associated_quantity(u);
@@ -241,6 +244,8 @@ template<Reference R1, Reference R2, Reference... Rest>
                              common_unit(get_unit(r1), get_unit(r2), get_unit(rest)...)>{};
 }
 
+MP_UNITS_EXPORT_END
+
 namespace detail {
 
 template<AssociatedUnit auto To, AssociatedUnit From>

src/core/include/mp-units/system_reference.h

@@ -23,10 +23,12 @@
 #pragma once
 
 #include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/quantity_spec.h>
 #include <mp-units/reference.h>
 #include <mp-units/unit.h>
 
+MP_UNITS_EXPORT
 namespace mp_units {
 
 /**

src/core/include/mp-units/unit.h

@@ -29,14 +29,18 @@
 #include <mp-units/bits/external/type_traits.h>
 #include <mp-units/bits/get_associated_quantity.h>
 #include <mp-units/bits/magnitude.h>
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/quantity_point_concepts.h>
 #include <mp-units/bits/quantity_spec_concepts.h>
 #include <mp-units/bits/ratio.h>
 #include <mp-units/bits/symbol_text.h>
 #include <mp-units/bits/text_tools.h>
 #include <mp-units/bits/unit_concepts.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <iterator>
-#include <string>
+#include <string_view>
+#endif
 
 namespace mp_units {
 
@@ -103,7 +107,7 @@ inline constexpr bool is_specialization_of_scaled_unit<scaled_unit<M, U>> = true
  *
  * @tparam Symbol a short text representation of the unit
  */
-template<basic_symbol_text Symbol, auto...>
+MP_UNITS_EXPORT template<basic_symbol_text Symbol, auto...>
 struct named_unit;
 
 /**
@@ -220,7 +224,7 @@ struct named_unit<Symbol, U, QS, PO> : std::remove_const_t<decltype(U)> {
  * @tparam M scaling factor of the prefix
  * @tparam U a named unit to be prefixed
  */
-template<basic_symbol_text Symbol, Magnitude auto M, PrefixableUnit auto U>
+MP_UNITS_EXPORT template<basic_symbol_text Symbol, Magnitude auto M, PrefixableUnit auto U>
   requires(!Symbol.empty())
 struct prefixed_unit : std::remove_const_t<decltype(M * U)> {
   static constexpr auto symbol = Symbol + U.symbol;
@@ -287,7 +291,7 @@ struct derived_unit : detail::expr_fractions<detail::is_one, Expr...> {};
  * Unit of a dimensionless quantity.
  */
 // clang-format off
-inline constexpr struct one : derived_unit<> {} one;
+MP_UNITS_EXPORT inline constexpr struct one : derived_unit<> {} one;
 // clang-format on
 
 namespace detail {
@@ -477,6 +481,7 @@ template<Unit Lhs, Unit Rhs>
 
 [[nodiscard]] MP_UNITS_CONSTEVAL Unit auto inverse(Unit auto u) { return one / u; }
 
+MP_UNITS_EXPORT_END
 
 namespace detail {
 
@@ -522,7 +527,7 @@ template<typename... Expr1, typename... Expr2>
 }  // namespace detail
 
 
-[[nodiscard]] consteval bool operator==(Unit auto lhs, Unit auto rhs)
+MP_UNITS_EXPORT [[nodiscard]] consteval bool operator==(Unit auto lhs, Unit auto rhs)
 {
   auto canonical_lhs = get_canonical_unit(lhs);
   auto canonical_rhs = get_canonical_unit(rhs);
@@ -540,6 +545,8 @@ inline constexpr bool is_specialization_of_derived_unit<derived_unit<Expr...>> =
 
 }  // namespace detail
 
+MP_UNITS_EXPORT_BEGIN
+
 /**
  * @brief Computes the value of a unit raised to the `Num/Den` power
  *
@@ -700,6 +707,8 @@ struct unit_symbol_formatting {
   unit_symbol_separator separator = unit_symbol_separator::default_separator;
 };
 
+MP_UNITS_EXPORT_END
+
 namespace detail {
 
 template<typename CharT, std::size_t N, std::size_t M, std::output_iterator<CharT> Out>
@@ -840,7 +849,7 @@ constexpr Out unit_symbol_impl(Out out, const derived_unit<Expr...>&, unit_symbo
 
 }  // namespace detail
 
-template<typename CharT = char, std::output_iterator<CharT> Out, Unit U>
+MP_UNITS_EXPORT template<typename CharT = char, std::output_iterator<CharT> Out, Unit U>
 constexpr Out unit_symbol_to(Out out, U u, unit_symbol_formatting fmt = unit_symbol_formatting{})
 {
   return detail::unit_symbol_impl<CharT>(out, u, fmt, false);
@@ -860,7 +869,7 @@ template<typename CharT, std::size_t N, unit_symbol_formatting fmt, Unit U>
 
 
 // TODO Refactor to `unit_symbol(U, fmt)` when P1045: constexpr Function Parameters is available
-template<unit_symbol_formatting fmt = unit_symbol_formatting{}, typename CharT = char, Unit U>
+MP_UNITS_EXPORT template<unit_symbol_formatting fmt = unit_symbol_formatting{}, typename CharT = char, Unit U>
 [[nodiscard]] consteval auto unit_symbol(U)
 {
   auto get_size = []() consteval {

src/core/mp-units-core.cpp

@@ -4,7 +4,6 @@ module;
 
 export module mp_units.core;
 
-export
-{
+#define MP_UNITS_IN_MODULE_INTERFACE
+
 #include <mp-units/core.h>
-}

src/systems/include/mp-units/systems/angular/math.h

@@ -22,18 +22,19 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/angular/units.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/bits/value_cast.h>
 #include <mp-units/customization_points.h>
 #include <mp-units/quantity.h>
 #include <mp-units/unit.h>
-#endif
-#include <mp-units/systems/angular/units.h>
-
-// IWYU pragma: begin_exports
 #include <cmath>
-// IWYU pragma: end_exports
+#endif
 
+
+MP_UNITS_EXPORT
 namespace mp_units::angular {
 
 template<ReferenceOf<angle> auto R, typename Rep>

src/systems/include/mp-units/systems/angular/units.h

@@ -22,12 +22,15 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/dimension.h>
 #include <mp-units/quantity_spec.h>
 #include <mp-units/unit.h>
 #endif
 
+MP_UNITS_EXPORT
 namespace mp_units::angular {
 
 // clang-format off

src/systems/include/mp-units/systems/cgs/cgs.h

@@ -22,11 +22,14 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/si/units.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/unit.h>
 #endif
-#include <mp-units/systems/si/units.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::cgs {
 
 // clang-format off

src/systems/include/mp-units/systems/hep/hep.h

@@ -22,15 +22,20 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/si/si.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/unit.h>
 #endif
-#include <mp-units/systems/si/si.h>
+
+MP_UNITS_EXPORT
+namespace mp_units {
 
 template<>
-inline constexpr std::optional<std::intmax_t> mp_units::known_first_factor<334'524'384'739> = 334'524'384'739;
+inline constexpr std::optional<std::intmax_t> known_first_factor<334'524'384'739> = 334'524'384'739;
 
-namespace mp_units::hep {
+namespace hep {
 
 // energy
 using si::electronvolt;
@@ -101,5 +106,5 @@ inline constexpr auto c = speed_of_light;
 inline constexpr auto c2 = square(speed_of_light);
 
 }  // namespace unit_symbols
-
-}  // namespace mp_units::hep
+}  // namespace hep
+}  // namespace mp_units

src/systems/include/mp-units/systems/iau/iau.h

@@ -22,12 +22,15 @@
 
 #pragma once
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
-#endif
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/units.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/unit.h>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units::iau {
 
 // https://en.wikipedia.org/wiki/Astronomical_system_of_units

src/systems/include/mp-units/systems/iec80000/binary_prefixes.h

@@ -22,6 +22,8 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/unit.h>
 #endif
@@ -38,6 +40,8 @@ template<PrefixableUnit U> struct exbi_ : prefixed_unit<"Ei", mag_power<2, 60>,
 template<PrefixableUnit U> struct zebi_ : prefixed_unit<"Zi", mag_power<2, 70>, U{}> {};
 template<PrefixableUnit U> struct yobi_ : prefixed_unit<"Yi", mag_power<2, 80>, U{}> {};
 
+MP_UNITS_EXPORT_BEGIN
+
 template<PrefixableUnit auto U> inline constexpr kibi_<std::remove_const_t<decltype(U)>> kibi;
 template<PrefixableUnit auto U> inline constexpr mebi_<std::remove_const_t<decltype(U)>> mebi;
 template<PrefixableUnit auto U> inline constexpr gibi_<std::remove_const_t<decltype(U)>> gibi;
@@ -48,4 +52,6 @@ template<PrefixableUnit auto U> inline constexpr zebi_<std::remove_const_t<declt
 template<PrefixableUnit auto U> inline constexpr yobi_<std::remove_const_t<decltype(U)>> yobi;
 // clang-format on
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units::iec80000

src/systems/include/mp-units/systems/iec80000/quantities.h

@@ -22,13 +22,16 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/isq/mechanics.h>
+#include <mp-units/systems/isq/space_and_time.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/dimension.h>
 #include <mp-units/quantity_spec.h>
 #endif
-#include <mp-units/systems/isq/mechanics.h>
-#include <mp-units/systems/isq/space_and_time.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::iec80000 {
 
 // dimensions of base quantities

src/systems/include/mp-units/systems/iec80000/unit_symbols.h

@@ -22,10 +22,12 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/iec80000/binary_prefixes.h>
 #include <mp-units/systems/iec80000/units.h>
 #include <mp-units/systems/si/prefixes.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::iec80000::unit_symbols {
 
 // bit

src/systems/include/mp-units/systems/iec80000/units.h

@@ -22,12 +22,15 @@
 
 #pragma once
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
-#endif
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/iec80000/quantities.h>
 #include <mp-units/systems/si/units.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/unit.h>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units::iec80000 {
 
 // clang-format off

src/systems/include/mp-units/systems/imperial/imperial.h

@@ -22,11 +22,14 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/international/international.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/unit.h>
 #endif
-#include <mp-units/systems/international/international.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::imperial {
 
 using namespace international;

src/systems/include/mp-units/systems/international/international.h

@@ -22,12 +22,15 @@
 
 #pragma once
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
-#endif
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/units.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/unit.h>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units::international {
 
 // clang-format off

src/systems/include/mp-units/systems/isq/atomic_and_nuclear_physics.h

@@ -22,11 +22,14 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/isq/si_quantities.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/quantity_spec.h>
 #endif
-#include <mp-units/systems/isq/si_quantities.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::isq {
 
 

src/systems/include/mp-units/systems/isq/base_quantities.h

@@ -22,12 +22,15 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/dimension.h>
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_spec.h>
 #endif
 
+MP_UNITS_EXPORT
 namespace mp_units::isq {
 
 // clang-format off

src/systems/include/mp-units/systems/isq/electromagnetism.h

@@ -22,13 +22,16 @@
 
 #pragma once
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
-#endif
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/isq/base_quantities.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/quantity_spec.h>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units::isq {
 
 QUANTITY_SPEC(electric_charge, electric_current* time);

src/systems/include/mp-units/systems/isq/mechanics.h

@@ -22,12 +22,15 @@
 
 #pragma once
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
-#endif
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/isq/si_quantities.h>
 #include <mp-units/systems/isq/space_and_time.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/quantity_spec.h>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units::isq {
 
 QUANTITY_SPEC(mass_density, mass / volume);

src/systems/include/mp-units/systems/isq/si_quantities.h

@@ -22,11 +22,14 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/isq/base_quantities.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/quantity_spec.h>
 #endif
-#include <mp-units/systems/isq/base_quantities.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::isq {
 
 // space and time

src/systems/include/mp-units/systems/isq/space_and_time.h

@@ -22,11 +22,14 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/isq/si_quantities.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/quantity_spec.h>
 #endif
-#include <mp-units/systems/isq/si_quantities.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::isq {
 
 QUANTITY_SPEC(height, length);

src/systems/include/mp-units/systems/isq/thermodynamics.h

@@ -22,13 +22,16 @@
 
 #pragma once
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
-#endif
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/si_quantities.h>
 #include <mp-units/systems/isq/space_and_time.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/quantity_spec.h>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units::isq {
 
 QUANTITY_SPEC(Celsius_temperature, thermodynamic_temperature);  // TODO should we account for T0 here?

src/systems/include/mp-units/systems/isq_angle/isq_angle.h

@@ -22,13 +22,16 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/angular/angular.h>
+#include <mp-units/systems/isq/isq.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/quantity_spec.h>
 #include <mp-units/reference.h>
 #endif
-#include <mp-units/systems/angular/angular.h>
-#include <mp-units/systems/isq/isq.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::isq_angle {
 
 using namespace isq;

src/systems/include/mp-units/systems/natural/natural.h

@@ -22,14 +22,17 @@
 
 #pragma once
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/system_reference.h>
-#include <mp-units/unit.h>
-#endif
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/prefixes.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/system_reference.h>
+#include <mp-units/unit.h>
+#endif
+
+MP_UNITS_EXPORT
 namespace mp_units::natural {
 
 // clang-format off

src/systems/include/mp-units/systems/si/chrono.h

@@ -22,14 +22,16 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/isq/space_and_time.h>
+#include <mp-units/systems/si/prefixes.h>
+#include <mp-units/systems/si/units.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/customization_points.h>
 #include <mp-units/quantity_point.h>
 #include <chrono>
 #endif
-#include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/prefixes.h>
-#include <mp-units/systems/si/units.h>
 
 namespace mp_units {
 
@@ -62,7 +64,7 @@ template<typename Period>
 
 }  // namespace detail
 
-template<typename Rep, typename Period>
+MP_UNITS_EXPORT template<typename Rep, typename Period>
 struct quantity_like_traits<std::chrono::duration<Rep, Period>> {
   static constexpr auto reference = detail::time_unit_from_chrono_period<Period>();
   using rep = Rep;
@@ -84,9 +86,10 @@ template<typename C>
 struct chrono_point_origin_ : absolute_point_origin<chrono_point_origin_<C>, isq::time> {
   using clock = C;
 };
-template<typename C>
+MP_UNITS_EXPORT template<typename C>
 inline constexpr chrono_point_origin_<C> chrono_point_origin;
 
+MP_UNITS_EXPORT_BEGIN
 
 template<typename C, typename Rep, typename Period>
 struct quantity_point_like_traits<std::chrono::time_point<C, std::chrono::duration<Rep, Period>>> {
@@ -111,7 +114,7 @@ struct quantity_point_like_traits<std::chrono::time_point<C, std::chrono::durati
 template<QuantityOf<isq::time> Q>
 [[nodiscard]] constexpr auto to_chrono_duration(const Q& q)
 {
-  constexpr auto canonical = detail::get_canonical_unit(Q::unit);
+  constexpr auto canonical = get_canonical_unit(Q::unit);
   constexpr ratio r = as_ratio(canonical.mag);
   return std::chrono::duration<typename Q::rep, std::ratio<r.num, r.den>>{q};
 }
@@ -122,10 +125,12 @@ template<QuantityPointOf<isq::time> QP>
 {
   using clock = MP_UNITS_TYPENAME decltype(QP::absolute_point_origin)::clock;
   using rep = MP_UNITS_TYPENAME QP::rep;
-  constexpr auto canonical = detail::get_canonical_unit(QP::unit);
+  constexpr auto canonical = get_canonical_unit(QP::unit);
   constexpr ratio r = as_ratio(canonical.mag);
   using ret_type = std::chrono::time_point<clock, std::chrono::duration<rep, std::ratio<r.num, r.den>>>;
   return ret_type(to_chrono_duration(qp - qp.absolute_point_origin));
 }
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units

src/systems/include/mp-units/systems/si/constants.h

@@ -22,11 +22,14 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/si/units.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/quantity.h>
 #endif
-#include <mp-units/systems/si/units.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::si {
 
 namespace si2019 {

src/systems/include/mp-units/systems/si/math.h

@@ -22,21 +22,21 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/isq/space_and_time.h>
+#include <mp-units/systems/si/units.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/bits/value_cast.h>
 #include <mp-units/customization_points.h>
 #include <mp-units/quantity.h>
 #include <mp-units/unit.h>
-#endif
-#include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/units.h>
-
-// IWYU pragma: begin_exports
 #include <cmath>
-// IWYU pragma: end_exports
+#endif
 
+
+MP_UNITS_EXPORT
 namespace mp_units::si {
-
 template<ReferenceOf<isq::angular_measure> auto R, typename Rep>
   requires requires(Rep v) { sin(v); } || requires(Rep v) { std::sin(v); }
 [[nodiscard]] inline QuantityOf<dimensionless> auto sin(const quantity<R, Rep>& q) noexcept

src/systems/include/mp-units/systems/si/prefixes.h

@@ -22,6 +22,8 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/unit.h>
 #endif
@@ -54,6 +56,8 @@ template<PrefixableUnit U> struct yotta_ : prefixed_unit<"Y", mag_power<10, 24>,
 template<PrefixableUnit U> struct ronna_ : prefixed_unit<"R", mag_power<10, 27>, U{}> {};
 template<PrefixableUnit U> struct quetta_ : prefixed_unit<"Q", mag_power<10, 30>, U{}> {};
 
+MP_UNITS_EXPORT_BEGIN
+
 template<PrefixableUnit auto U> inline constexpr quecto_<std::remove_const_t<decltype(U)>> quecto;
 template<PrefixableUnit auto U> inline constexpr ronto_<std::remove_const_t<decltype(U)>> ronto;
 template<PrefixableUnit auto U> inline constexpr yocto_<std::remove_const_t<decltype(U)>> yocto;
@@ -80,4 +84,6 @@ template<PrefixableUnit auto U> inline constexpr ronna_<std::remove_const_t<decl
 template<PrefixableUnit auto U> inline constexpr quetta_<std::remove_const_t<decltype(U)>> quetta;
 // clang-format on
 
+MP_UNITS_EXPORT_END
+
 }  // namespace mp_units::si

src/systems/include/mp-units/systems/si/unit_symbols.h

@@ -22,9 +22,11 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/si/prefixes.h>
 #include <mp-units/systems/si/units.h>
 
+MP_UNITS_EXPORT
 namespace mp_units {
 
 namespace si::unit_symbols {

src/systems/include/mp-units/systems/si/units.h

@@ -22,14 +22,16 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/isq/si_quantities.h>
+#include <mp-units/systems/si/prefixes.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/quantity_point.h>
 #include <mp-units/unit.h>
 #endif
-// #include <mp-units/systems/isq/mechanics.h>
-#include <mp-units/systems/isq/si_quantities.h>
-#include <mp-units/systems/si/prefixes.h>
 
+MP_UNITS_EXPORT
 namespace mp_units {
 
 namespace si {
@@ -58,20 +60,17 @@ inline constexpr struct radian : named_unit<"rad", metre / metre, kind_of<isq::a
 inline constexpr struct steradian : named_unit<"sr", square(metre) / square(metre), kind_of<isq::solid_angular_measure>> {} steradian;
 inline constexpr struct hertz : named_unit<"Hz", one / second, kind_of<isq::frequency>> {} hertz;
 inline constexpr struct newton : named_unit<"N", kilogram * metre / square(second)> {} newton;
-// inline constexpr struct newton : named_unit<"N", kilogram * metre / square(second), kind_of<isq::force>> {} newton;
 #ifdef pascal
 #pragma push_macro("pascal")
 #undef pascal
 #define MP_UNITS_REDEFINE_PASCAL
 #endif
 inline constexpr struct pascal : named_unit<"Pa", newton / square(metre)> {} pascal;
-// inline constexpr struct pascal : named_unit<"Pa", newton / square(metre), kind_of<isq::pressure>> {} pascal;
 #ifdef MP_UNITS_REDEFINE_PASCAL
 #pragma pop_macro("pascal")
 #undef MP_UNITS_REDEFINE_PASCAL
 #endif
 inline constexpr struct joule : named_unit<"J", newton * metre> {} joule;
-// inline constexpr struct joule : named_unit<"J", newton * metre, kind_of<isq::energy>> {} joule;
 inline constexpr struct watt : named_unit<"W", joule / second> {} watt;
 inline constexpr struct coulomb : named_unit<"C", ampere * second> {} coulomb;
 inline constexpr struct volt : named_unit<"V", watt / ampere> {} volt;

src/systems/include/mp-units/systems/typographic/typographic.h

@@ -22,11 +22,14 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/international/international.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/unit.h>
 #endif
-#include <mp-units/systems/international/international.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::typographic {
 
 // clang-format off

src/systems/include/mp-units/systems/usc/usc.h

@@ -22,11 +22,14 @@
 
 #pragma once
 
+#include <mp-units/bits/module_macros.h>
+#include <mp-units/systems/international/international.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/unit.h>
 #endif
-#include <mp-units/systems/international/international.h>
 
+MP_UNITS_EXPORT
 namespace mp_units::usc {
 
 using namespace international;

src/systems/mp-units-systems.cpp

@@ -7,8 +7,6 @@ export module mp_units.systems;
 
 export import mp_units.core;
 
-export
-{
 #define MP_UNITS_IN_MODULE_INTERFACE
 
 #include <mp-units/systems/angular/angular.h>
@@ -24,4 +22,3 @@ export
 #include <mp-units/systems/si/si.h>
 #include <mp-units/systems/typographic/typographic.h>
 #include <mp-units/systems/usc/usc.h>
-}

test/static/CMakeLists.txt

@@ -23,9 +23,6 @@
 cmake_minimum_required(VERSION 3.5)
 
 add_library(unit_tests_static_truncating quantity_test.cpp)
-if(${projectPrefix}BUILD_CXX_MODULES)
-    target_compile_definitions(unit_tests_static_truncating PUBLIC ${projectPrefix}MODULES)
-endif()
 target_link_libraries(unit_tests_static_truncating PRIVATE mp-units::mp-units)
 target_compile_options(
     unit_tests_static_truncating PRIVATE $<IF:$<CXX_COMPILER_ID:MSVC>,/wd4242 /wd4244,-Wno-conversion>
@@ -68,7 +65,4 @@ add_library(
 )
 
 target_link_libraries(unit_tests_static PRIVATE mp-units::mp-units)
-if(${projectPrefix}BUILD_CXX_MODULES)
-    target_compile_definitions(unit_tests_static PUBLIC ${projectPrefix}MODULES)
-endif()
 target_link_libraries(unit_tests_static PRIVATE unit_tests_static_truncating)

test/static/angular_test.cpp

@@ -20,12 +20,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <numbers>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/systems/isq_angle/isq_angle.h>
-#endif
+#include <numbers>
 
 namespace {
 

test/static/cgs_test.cpp

@@ -21,14 +21,10 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/systems/cgs/cgs.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#endif
 
 template<class T>
   requires mp_units::is_scalar<T>

test/static/chrono_test.cpp

@@ -21,15 +21,10 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <ratio>
-#ifdef MP_UNITS_MODULES
-#include <chrono>
-import mp_units;
-#else
 #include <mp-units/bits/external/type_traits.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/si/si.h>
-#endif
+#include <ratio>
 
 namespace {
 

test/static/compare_test.cpp

@@ -20,12 +20,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/compare.h>
 #include <mp-units/systems/si/si.h>
-#endif
 
 namespace {
 

test/static/concepts_test.cpp

@@ -20,19 +20,15 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <chrono>
-#include <complex>
-#include <optional>
-#include <string>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/concepts.h>
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/natural/natural.h>
 #include <mp-units/systems/si/si.h>
-#endif
+#include <chrono>
+#include <complex>
+#include <optional>
+#include <string>
 
 template<typename T>
 inline constexpr bool mp_units::is_scalar<std::complex<T>> = true;

test/static/custom_rep_test_min_impl.cpp

@@ -21,13 +21,9 @@
 // SOFTWARE.
 
 #include <mp-units/bits/external/hacks.h>
+#include <mp-units/systems/si/units.h>
 #include <concepts>
 #include <type_traits>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
-#include <mp-units/systems/si/units.h>
-#endif
 
 namespace {
 

test/static/dimension_test.cpp

@@ -21,15 +21,11 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/dimension.h>
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_spec.h>
 #include <mp-units/reference.h>
 #include <mp-units/unit.h>
-#endif
 
 namespace {
 

test/static/fixed_string_test.cpp

@@ -20,11 +20,7 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/bits/external/fixed_string.h>
-#endif
 
 using namespace mp_units;
 

test/static/fractional_exponent_quantity.cpp

@@ -21,13 +21,9 @@
 // SOFTWARE.
 
 #include <mp-units/compat_macros.h>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/math.h>
 #include <mp-units/systems/isq/electromagnetism.h>
 #include <mp-units/systems/si/units.h>
-#endif
 
 namespace {
 

test/static/hep_test.cpp

@@ -20,14 +20,10 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/systems/hep/hep.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
-#endif
 
 template<class T>
   requires mp_units::is_scalar<T>

test/static/iau_test.cpp

@@ -20,14 +20,10 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/math.h>
 #include <mp-units/systems/iau/iau.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
-#endif
 
 /* ************** DERIVED DIMENSIONS THAT INCLUDE UNITS WITH SPECIAL NAMES **************** */
 

test/static/iec80000_test.cpp

@@ -20,14 +20,10 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/quantity.h>
 #include <mp-units/reference.h>
 #include <mp-units/systems/iec80000/iec80000.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#endif
 
 /* ************** DERIVED DIMENSIONS THAT INCLUDE UNITS WITH SPECIAL NAMES **************** */
 

test/static/imperial_test.cpp

@@ -20,13 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/systems/imperial/imperial.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#endif
 
 namespace {
 

test/static/international_test.cpp

@@ -20,16 +20,12 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/math.h>
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/units.h>
-#endif
 
 template<class T>
   requires mp_units::is_scalar<T>

test/static/isq_angle_test.cpp

@@ -20,12 +20,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/systems/isq_angle/isq_angle.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#endif
 
 namespace {
 

test/static/isq_test.cpp

@@ -20,13 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/reference.h>
 #include <mp-units/systems/isq/isq.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#endif
 
 namespace {
 

test/static/math_test.cpp

@@ -21,14 +21,10 @@
 // SOFTWARE.
 
 #include <optional>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/math.h>  // IWYU pragma: keep
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
-#endif
 
 namespace {
 

test/static/natural_test.cpp

@@ -20,12 +20,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/math.h>
 #include <mp-units/systems/natural/natural.h>
-#endif
 
 template<class T>
   requires mp_units::is_scalar<T>

test/static/prime_test.cpp

@@ -20,13 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/bits/external/prime.h>
 #include <type_traits>
 #include <utility>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
-#include <mp-units/bits/external/prime.h>
-#endif
 
 using namespace mp_units::detail;
 

test/static/quantity_point_test.cpp

@@ -24,15 +24,10 @@
 #include <limits>
 #include <type_traits>
 #include <utility>
-#ifdef MP_UNITS_MODULES
-#include <chrono>
-import mp_units;
-#else
 #include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/isq.h>
 #include <mp-units/systems/si/si.h>
 #include <mp-units/systems/usc/usc.h>
-#endif
 
 namespace {
 

test/static/quantity_spec_test.cpp

@@ -21,14 +21,10 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_spec.h>
 #include <mp-units/reference.h>
 #include <mp-units/unit.h>
-#endif
 
 namespace {
 

test/static/quantity_test.cpp

@@ -20,19 +20,13 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/bits/external/hacks.h>
-//
 #include "test_tools.h"
-#include <limits>
-#include <utility>
-#ifdef MP_UNITS_MODULES
-#include <chrono>
-import mp_units;
-#else
+#include <mp-units/bits/external/hacks.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
-#endif
+#include <limits>
+#include <utility>
 
 template<>
 inline constexpr bool mp_units::is_vector<int> = true;

test/static/ratio_test.cpp

@@ -20,11 +20,7 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/bits/ratio.h>
-#endif
 
 namespace {
 

test/static/reference_test.cpp

@@ -21,9 +21,6 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/dimension.h>
 #include <mp-units/quantity.h>
 #include <mp-units/quantity_spec.h>
@@ -31,7 +28,6 @@ import mp_units;
 #include <mp-units/system_reference.h>
 #include <mp-units/systems/si/prefixes.h>
 #include <mp-units/unit.h>
-#endif
 
 namespace {
 

test/static/si_test.cpp

@@ -21,12 +21,8 @@
 // SOFTWARE.
 
 #include <type_traits>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/math.h>
 #include <mp-units/systems/si/si.h>
-#endif
 
 namespace {
 

test/static/symbol_text_test.cpp

@@ -20,11 +20,7 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/bits/symbol_text.h>
-#endif
 
 using namespace mp_units;
 

test/static/test_tools.h

@@ -23,12 +23,7 @@
 #pragma once
 
 #include <type_traits>
-#ifdef MP_UNITS_MODULES
-#include <mp-units/compat_macros.h>
-import mp_units;
-#else
 #include <mp-units/quantity_spec.h>
-#endif
 
 template<auto V, typename T>
 inline constexpr bool is_of_type = std::is_same_v<std::remove_cvref_t<decltype(V)>, T>;

test/static/type_list_test.cpp

@@ -20,13 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <type_traits>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/bits/external/type_list.h>
 #include <mp-units/bits/external/type_traits.h>
-#endif
+#include <type_traits>
 
 namespace {
 

test/static/typographic_test.cpp

@@ -20,13 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/typographic/typographic.h>
-#endif
 
 namespace {
 

test/static/unit_symbol_test.cpp

@@ -20,13 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/systems/iau/iau.h>
 #include <mp-units/systems/iec80000/iec80000.h>
 #include <mp-units/systems/si/si.h>
-#endif
 
 namespace {
 

test/static/unit_test.cpp

@@ -21,15 +21,11 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/dimension.h>
 #include <mp-units/quantity.h>
 #include <mp-units/reference.h>
 #include <mp-units/systems/si/prefixes.h>
 #include <mp-units/unit.h>
-#endif
 
 namespace {
 

test/static/usc_test.cpp

@@ -21,14 +21,10 @@
 // SOFTWARE.
 
 #include <mp-units/bits/external/hacks.h>
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
 #include <mp-units/systems/usc/usc.h>
-#endif
 
 namespace {