build: Added an option to disable UDLs support

Now it is time to get rid of UDLs from tests and examples and then disable them by default.

conanfile.py

@@ -41,10 +41,12 @@ class UnitsConan(ConanFile):
         "gsl-lite/0.37.0"
     )
     options = {
+        "udls": [True, False],
         "downcast_mode": ["off", "on", "auto"],
         "build_docs": [True, False]
     }
     default_options = {
+        "udls": True,
         "downcast_mode": "on",
         "build_docs": True
     }
@@ -116,6 +118,7 @@ class UnitsConan(ConanFile):
 
     def generate(self):
         tc = CMakeToolchain(self)
+        tc.variables["UNITS_UDLS"] = self.options.udls
         tc.variables["UNITS_DOWNCAST_MODE"] = str(self.options.downcast_mode).upper()
         # if self._run_tests:  # TODO Enable this when environment is supported in the Conan toolchain
         tc.variables["UNITS_BUILD_DOCS"] = self.options.build_docs

docs/usage.rst

@@ -123,6 +123,15 @@ It also runs unit tests during Conan build.
 Conan Options
 ^^^^^^^^^^^^^
 
+udls
+++++
+
+**Values**: ``True``/``False``
+
+**Defaulted to**: ``True``
+
+Determines if library should provide User Defined Literals (UDLs) for quantities of various units.
+
 downcast_mode
 +++++++++++++
 
@@ -149,6 +158,16 @@ Additionally, enables project documentation generation when the project is being
 CMake Options
 ^^^^^^^^^^^^^
 
+UNITS_UDLS
++++++++++++++++++++
+
+**Values**: ``ON``/``OFF``
+
+**Defaulted to**: ``ON``
+
+Equivalent to `udls`_.
+
+
 UNITS_DOWNCAST_MODE
 +++++++++++++++++++
 

src/CMakeLists.txt

@@ -27,15 +27,20 @@ project(mp-units
 )
 
 option(UNITS_AS_SYSTEM_HEADERS "Exports library as system headers" OFF)
-if(UNITS_AS_SYSTEM_HEADERS)
-    set(units_as_system SYSTEM)
-endif()
+option(UNITS_UDLS "Enables definitions of User Defined Literals (UDLs) provided for quantities of various units" ON)
+
+message(STATUS "UNITS_AS_SYSTEM_HEADERS: ${UNITS_AS_SYSTEM_HEADERS}")
+message(STATUS "UNITS_UDLS: ${UNITS_UDLS}")
 
 list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
 
 include(AddUnitsModule)
 include(GNUInstallDirs)
 
+if(UNITS_AS_SYSTEM_HEADERS)
+    set(units_as_system SYSTEM)
+endif()
+
 add_subdirectory(core)
 add_subdirectory(core-fmt)
 add_subdirectory(core-io)

src/cmake/AddUnitsModule.cmake

@@ -38,3 +38,14 @@ function(add_units_module name)
     install(TARGETS mp-units-${name} EXPORT mp-unitsTargets)
     install(DIRECTORY include/units TYPE INCLUDE)
 endfunction()
+
+
+#
+# add_units_systems(ModuleName <depependencies>...)
+#
+function(add_units_system name)
+    add_units_module(${name} ${ARGN})
+    if(UNITS_UDLS)
+        target_compile_definitions(mp-units-${name} INTERFACE UNITS_UDLS=1)
+    endif()
+endfunction()

src/core/CMakeLists.txt

@@ -55,6 +55,10 @@ elseif(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
     )
 endif()
 
+if(UNITS_UDLS)
+    target_compile_definitions(mp-units-core INTERFACE UNITS_UDLS=1)
+endif()
+
 if(DEFINED UNITS_DOWNCAST_MODE)
     set(downcast_mode_options OFF ON AUTO)
     list(FIND downcast_mode_options "${UNITS_DOWNCAST_MODE}" downcast_mode)

src/core/include/units/generic/angle.h

@@ -43,6 +43,8 @@ concept Angle = QuantityOfT<T, dim_angle>;
 template<UnitOf<dim_angle<>> U, Representation Rep = double>
 using angle = quantity<dim_angle<>, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // rad
@@ -51,6 +53,8 @@ constexpr auto operator"" _q_rad(long double l) { return angle<radian, long doub
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto rad = reference<dim_angle<>, radian>{};

src/systems/isq-iec80000/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(isq-iec80000 mp-units::si)
+add_units_system(isq-iec80000 mp-units::si)

src/systems/isq-iec80000/include/units/isq/iec80000/modulation_rate.h

@@ -50,6 +50,8 @@ using dim_modulation_rate = si::dim_frequency;
 template<UnitOf<dim_modulation_rate> U, Representation Rep = double>
 using modulation_rate = quantity<dim_modulation_rate, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 constexpr auto operator"" _q_Bd(unsigned long long l) { gsl_ExpectsAudit(std::in_range<std::int64_t>(l)); return modulation_rate<baud, std::int64_t>(static_cast<std::int64_t>(l)); }
@@ -64,6 +66,8 @@ constexpr auto operator"" _q_YBd(unsigned long long l) { gsl_ExpectsAudit(std::i
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto Bd = reference<dim_modulation_rate, baud>{};

src/systems/isq-iec80000/include/units/isq/iec80000/storage_capacity.h

@@ -79,6 +79,8 @@ concept StorageCapacity = QuantityOf<T, dim_storage_capacity>;
 template<UnitOf<dim_storage_capacity> U, Representation Rep = double>
 using storage_capacity = quantity<dim_storage_capacity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // bits
@@ -121,6 +123,8 @@ constexpr auto operator"" _q_PiB(unsigned long long l) { gsl_ExpectsAudit(std::i
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 // bits

src/systems/isq-iec80000/include/units/isq/iec80000/traffic_intensity.h

@@ -43,12 +43,16 @@ concept TrafficIntensity = QuantityOf<T, dim_traffic_intensity>;
 template<UnitOf<dim_traffic_intensity> U, Representation Rep = double>
 using traffic_intensity = quantity<dim_traffic_intensity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 constexpr auto operator"" _q_E(unsigned long long l) { gsl_ExpectsAudit(std::in_range<std::int64_t>(l)); return traffic_intensity<erlang, std::int64_t>(static_cast<std::int64_t>(l)); }
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto E = reference<dim_traffic_intensity, erlang>{};

src/systems/isq-iec80000/include/units/isq/iec80000/transfer_rate.h

@@ -52,6 +52,8 @@ concept TransferRate = QuantityOf<T, dim_transfer_rate>;
 template<UnitOf<dim_transfer_rate> U, Representation Rep = double>
 using transfer_rate = quantity<dim_transfer_rate, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 constexpr auto operator"" _q_B_per_s(unsigned long long l) { gsl_ExpectsAudit(std::in_range<std::int64_t>(l)); return transfer_rate<byte_per_second, std::int64_t>(static_cast<std::int64_t>(l)); }
@@ -66,4 +68,6 @@ constexpr auto operator"" _q_YB_per_s(unsigned long long l) { gsl_ExpectsAudit(s
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::iec80000

src/systems/isq-natural/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(isq-natural mp-units::isq)
+add_units_system(isq-natural mp-units::isq)

src/systems/si-cgs/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(si-cgs mp-units::si)
+add_units_system(si-cgs mp-units::si)

src/systems/si-cgs/include/units/isq/si/cgs/acceleration.h

@@ -40,6 +40,8 @@ struct dim_acceleration : isq::dim_acceleration<dim_acceleration, gal, dim_lengt
 template<UnitOf<dim_acceleration> U, Representation Rep = double>
 using acceleration = quantity<dim_acceleration, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Gal
@@ -48,6 +50,8 @@ constexpr auto operator"" _q_Gal(long double l) { return acceleration<gal, long
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto Gal = reference<dim_acceleration, gal>{};

src/systems/si-cgs/include/units/isq/si/cgs/area.h

@@ -42,6 +42,8 @@ struct dim_area : isq::dim_area<dim_area, square_centimetre, dim_length> {};
 template<UnitOf<dim_area> U, Representation Rep = double>
 using area = quantity<dim_area, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // cm2
@@ -50,6 +52,8 @@ constexpr auto operator"" _q_cm2(long double l) { return area<square_centimetre,
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto cm2 = reference<dim_area, square_centimetre>{};

src/systems/si-cgs/include/units/isq/si/cgs/energy.h

@@ -42,6 +42,8 @@ struct dim_energy : isq::dim_energy<dim_energy, erg, dim_force, dim_length> {};
 template<UnitOf<dim_energy> U, Representation Rep = double>
 using energy = quantity<dim_energy, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // erg
@@ -50,6 +52,8 @@ constexpr auto operator"" _q_erg(long double l) { return energy<erg, long double
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto erg = reference<dim_energy, cgs::erg>{};

src/systems/si-cgs/include/units/isq/si/cgs/force.h

@@ -43,6 +43,8 @@ struct dim_force : isq::dim_force<dim_force, dyne, dim_mass, dim_acceleration> {
 template<UnitOf<dim_force> U, Representation Rep = double>
 using force = quantity<dim_force, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // dyn
@@ -51,6 +53,8 @@ constexpr auto operator"" _q_dyn(long double l) { return force<dyne, long double
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto dyn = reference<dim_force, dyne>{};

src/systems/si-cgs/include/units/isq/si/cgs/length.h

@@ -41,6 +41,8 @@ struct dim_length : isq::dim_length<centimetre> {};
 template<UnitOf<dim_length> U, Representation Rep = double>
 using length = quantity<dim_length, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // cm
@@ -49,6 +51,8 @@ constexpr auto operator"" _q_cm(long double l) { return length<centimetre, long
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto cm = reference<dim_length, centimetre>{};

src/systems/si-cgs/include/units/isq/si/cgs/mass.h

@@ -41,6 +41,8 @@ struct dim_mass : isq::dim_mass<gram> {};
 template<UnitOf<dim_mass> U, Representation Rep = double>
 using mass = quantity<dim_mass, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // g
@@ -49,6 +51,8 @@ constexpr auto operator"" _q_g(long double l) { return mass<gram, long double>(l
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto g = reference<dim_mass, gram>{};

src/systems/si-cgs/include/units/isq/si/cgs/power.h

@@ -41,6 +41,8 @@ struct dim_power : isq::dim_power<dim_power, erg_per_second, dim_energy, dim_tim
 template<UnitOf<dim_power> U, Representation Rep = double>
 using power = quantity<dim_power, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // erg/s
@@ -49,4 +51,6 @@ constexpr auto operator"" _q_erg_per_s(long double l) { return power<erg_per_sec
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si::cgs

src/systems/si-cgs/include/units/isq/si/cgs/pressure.h

@@ -43,6 +43,8 @@ struct dim_pressure : isq::dim_pressure<dim_pressure, barye, dim_force, dim_area
 template<UnitOf<dim_pressure> U, Representation Rep = double>
 using pressure = quantity<dim_pressure, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Ba
@@ -51,6 +53,8 @@ constexpr auto operator"" _q_Ba(long double l) { return pressure<barye, long dou
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto Ba = reference<dim_pressure, barye>{};

src/systems/si-cgs/include/units/isq/si/cgs/speed.h

@@ -40,6 +40,8 @@ struct dim_speed : isq::dim_speed<dim_speed, centimetre_per_second, dim_length,
 template<UnitOf<dim_speed> U, Representation Rep = double>
 using speed = quantity<dim_speed, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // cm/s
@@ -48,4 +50,6 @@ constexpr auto operator"" _q_cm_per_s(long double l) { return speed<centimetre_p
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si::cgs

src/systems/si-cgs/include/units/isq/si/cgs/time.h

@@ -37,12 +37,16 @@ using si::second;
 using si::dim_time;
 using si::time;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 using si::literals::operator"" _q_s;
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 using si::references::s;

src/systems/si-fps/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(si-fps mp-units::si)
+add_units_system(si-fps mp-units::si)

src/systems/si-fps/include/units/isq/si/fps/acceleration.h

@@ -39,6 +39,8 @@ struct dim_acceleration : isq::dim_acceleration<dim_acceleration, foot_per_secon
 template<UnitOf<dim_acceleration> U, Representation Rep = double>
 using acceleration = quantity<dim_acceleration, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ft/s2
@@ -47,4 +49,6 @@ constexpr auto operator"" _q_ft_per_s2(long double l) { return acceleration<foot
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si::fps

src/systems/si-fps/include/units/isq/si/fps/area.h

@@ -41,6 +41,8 @@ struct dim_area : isq::dim_area<dim_area, square_foot, dim_length> {};
 template<UnitOf<dim_area> U, Representation Rep = double>
 using area = quantity<dim_area, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ft2
@@ -49,6 +51,8 @@ constexpr auto operator"" _q_ft2(long double l) { return area<square_foot, long
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto ft2 = reference<dim_area, square_foot>{};

src/systems/si-fps/include/units/isq/si/fps/density.h

@@ -41,6 +41,8 @@ struct dim_density : isq::dim_density<dim_density, pound_per_foot_cub, dim_mass,
 template<UnitOf<dim_density> U, Representation Rep = double>
 using density = quantity<dim_density, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // lb/ft³
@@ -49,4 +51,6 @@ constexpr auto operator"" _q_lb_per_ft3(long double l) { return density<pound_pe
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si::fps

src/systems/si-fps/include/units/isq/si/fps/energy.h

@@ -45,6 +45,8 @@ struct foot_pound_force : noble_deduced_unit<foot_pound_force, dim_energy, pound
 template<UnitOf<dim_energy> U, Representation Rep = double>
 using energy = quantity<dim_energy, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // foot poundal
@@ -57,4 +59,6 @@ constexpr auto operator"" _q_ft_lbf(long double l) { return energy<foot_pound_fo
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si::fps

src/systems/si-fps/include/units/isq/si/fps/force.h

@@ -52,6 +52,8 @@ struct dim_force : isq::dim_force<dim_force, poundal, dim_mass, dim_acceleration
 template<UnitOf<dim_force> U, Representation Rep = double>
 using force = quantity<dim_force, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // poundal
@@ -68,6 +70,8 @@ constexpr auto operator"" _q_klbf(long double l) { return force<kilopound_force,
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto pdl = reference<dim_force, poundal>{};

src/systems/si-fps/include/units/isq/si/fps/length.h

@@ -59,6 +59,8 @@ struct dim_length : isq::dim_length<foot> {};
 template<UnitOf<dim_length> U, Representation Rep = double>
 using length = quantity<dim_length, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Thousandth
@@ -98,6 +100,8 @@ constexpr auto operator"" _q_naut_mi(long double l) { return length<nautical_mil
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto thou = reference<dim_length, thousandth>{};

src/systems/si-fps/include/units/isq/si/fps/mass.h

@@ -58,6 +58,8 @@ struct short_ton : named_scaled_unit<short_ton, "ton (short)", no_prefix, ratio(
 
 struct long_ton : named_scaled_unit<long_ton, "ton (long)", no_prefix, ratio(2'240, 1), pound>{};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Grain
@@ -98,6 +100,8 @@ constexpr auto operator"" _q_lton(long double l) { return mass<long_ton, long do
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto gr = reference<dim_mass, grain>{};

src/systems/si-fps/include/units/isq/si/fps/power.h

@@ -46,6 +46,8 @@ struct horse_power : named_scaled_unit<horse_power, "hp", no_prefix, ratio(550),
 template<UnitOf<dim_power> U, Representation Rep = double>
 using power = quantity<dim_power, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // foot pound force per second
@@ -62,6 +64,8 @@ constexpr auto operator"" _q_hp(long double l) { return power<horse_power, long
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto hp = reference<dim_power, horse_power>{};

src/systems/si-fps/include/units/isq/si/fps/pressure.h

@@ -49,6 +49,8 @@ struct pound_force_per_inch_sq : named_scaled_unit<pound_force_per_inch_sq, "psi
 
 struct kilopound_force_per_inch_sq : prefixed_unit<kilopound_force_per_inch_sq, si::kilo, pound_force_per_inch_sq> {};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Poundal per square foot
@@ -65,6 +67,8 @@ constexpr auto operator"" _q_kpsi(long double l) { return pressure<kilopound_for
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto psi = reference<dim_pressure, pound_force_per_inch_sq>{};

src/systems/si-fps/include/units/isq/si/fps/speed.h

@@ -48,6 +48,8 @@ struct nautical_mile_per_hour : named_deduced_unit<nautical_mile_per_hour, dim_s
 struct knot : alias_unit<nautical_mile_per_hour, "knot", no_prefix> {};
 
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ft/s
@@ -64,6 +66,8 @@ constexpr auto operator"" _q_knot(long double l) { return speed<knot, long doubl
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto mph = reference<dim_speed, mile_per_hour>{};

src/systems/si-fps/include/units/isq/si/fps/time.h

@@ -41,12 +41,16 @@ using si::hour;
 using si::dim_time;
 using si::time;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 using si::literals::operator"" _q_s;
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 using si::references::s;

src/systems/si-fps/include/units/isq/si/fps/volume.h

@@ -42,6 +42,8 @@ struct cubic_yard : deduced_unit<cubic_yard, dim_volume, yard> {};
 template<UnitOf<dim_volume> U, Representation Rep = double>
 using volume = quantity<dim_volume, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ft3
@@ -54,6 +56,8 @@ constexpr auto operator"" _q_yd3(long double l) { return volume<cubic_yard, long
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto ft3 = reference<dim_volume, cubic_foot>{};

src/systems/si-iau/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(si-iau mp-units::si)
+add_units_system(si-iau mp-units::si)

src/systems/si-iau/include/units/isq/si/iau/length.h

@@ -44,6 +44,8 @@ struct parsec : named_scaled_unit<parsec, "pc", si::prefix, ratio(30'856'775'814
 // https://en.wikipedia.org/wiki/Angstrom
 struct angstrom : named_scaled_unit<angstrom, "angstrom", no_prefix, ratio(1, 1, -10), si::metre> {};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ly
@@ -60,6 +62,8 @@ constexpr auto operator"" _q_angstrom(long double l) { return si::length<angstro
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto ly = reference<si::dim_length, light_year>{};

src/systems/si-imperial/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(si-imperial mp-units::si)
+add_units_system(si-imperial mp-units::si)

src/systems/si-imperial/include/units/isq/si/imperial/length.h

@@ -40,6 +40,8 @@ struct chain : named_scaled_unit<chain, "ch", no_prefix, ratio(22, 1), si::inter
 // https://en.wikipedia.org/wiki/Rod_(unit)
 struct rod : named_scaled_unit<rod, "rd", no_prefix, ratio(1, 4), chain> {};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ch
@@ -52,6 +54,8 @@ constexpr auto operator"" _q_rd(long double l) { return si::length<rod, long dou
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto ch = reference<si::dim_length, chain>{};

src/systems/si-international/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(si-international mp-units::si)
+add_units_system(si-international mp-units::si)

src/systems/si-international/include/units/isq/si/international/area.h

@@ -37,6 +37,8 @@ namespace units::isq::si::international {
 
 struct square_foot : deduced_unit<square_foot, si::dim_area, si::international::foot> {};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ft2
@@ -45,6 +47,8 @@ constexpr auto operator"" _q_ft2(long double l) { return si::area<square_foot, l
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto ft2 = reference<si::dim_area, square_foot>{};

src/systems/si-international/include/units/isq/si/international/length.h

@@ -66,6 +66,8 @@ struct thou : named_scaled_unit<thou, "thou", no_prefix, ratio(1, 1000), inch> {
 // https://en.wikipedia.org/wiki/Thousandth_of_an_inch
 using mil = thou;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // yd
@@ -102,6 +104,8 @@ constexpr auto operator"" _q_mil(long double l) { return si::length<mil, long do
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto yd = reference<si::dim_length, yard>{};

src/systems/si-international/include/units/isq/si/international/speed.h

@@ -36,6 +36,8 @@ namespace units::isq::si::international {
 
 struct mile_per_hour : deduced_unit<mile_per_hour, si::dim_speed, si::international::mile, si::hour> {};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // mi/h
@@ -44,4 +46,6 @@ constexpr auto operator"" _q_mi_per_h(long double l) { return si::speed<mile_per
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si::international

src/systems/si-international/include/units/isq/si/international/volume.h

@@ -37,6 +37,8 @@ namespace units::isq::si::international {
 
 struct cubic_foot : deduced_unit<cubic_foot, si::dim_volume, si::international::foot> {};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ft3
@@ -45,6 +47,8 @@ constexpr auto operator"" _q_ft3(long double l) { return si::volume<cubic_foot,
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto ft3 = reference<si::dim_volume, cubic_foot>{};

src/systems/si-typographic/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(si-typographic mp-units::si)
+add_units_system(si-typographic mp-units::si)

src/systems/si-typographic/include/units/isq/si/typographic/length.h

@@ -41,6 +41,8 @@ struct pica_prn : named_scaled_unit<pica_prn, "pica(prn)", no_prefix, ratio(2108
 struct point_comp : named_scaled_unit<point_comp, "point(comp)", no_prefix, ratio(1763889, 500000, -4), si::metre> {};
 struct point_prn : named_scaled_unit<point_prn, "point(prn)", no_prefix, ratio(1757299, 500000, -4), si::metre> {};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // pica comp
@@ -61,6 +63,8 @@ constexpr auto operator"" _q_point_prn(long double l) { return si::length<point_
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto pica_comp = reference<si::dim_length, typographic::pica_comp>{};

src/systems/si-us/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(si-us mp-units::si)
+add_units_system(si-us mp-units::si)

src/systems/si-us/include/units/isq/si/us/length.h

@@ -45,6 +45,8 @@ struct fathom : named_scaled_unit<fathom, "fathom(us)", no_prefix, ratio(6), foo
 // https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors#B6
 struct mile : named_scaled_unit<mile, "mi(us)", no_prefix, ratio(5280), foot> {};
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ft
@@ -61,6 +63,8 @@ constexpr auto operator"" _q_mi_us(long double l) { return si::length<units::isq
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto ft = reference<si::dim_length, us::foot>{};

src/systems/si/CMakeLists.txt

@@ -22,4 +22,4 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_units_module(si mp-units::isq)
+add_units_system(si mp-units::isq)

src/systems/si/include/units/isq/si/absorbed_dose.h

@@ -62,6 +62,8 @@ struct dim_absorbed_dose : isq::dim_absorbed_dose<dim_absorbed_dose, gray, dim_e
 template<UnitOf<dim_absorbed_dose> U, Representation Rep = double>
 using absorbed_dose = quantity<dim_absorbed_dose, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Gy
@@ -150,6 +152,8 @@ constexpr auto operator"" _q_YGy(long double l) { return absorbed_dose<yottagray
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto Gy = reference<dim_absorbed_dose, gray>{};

src/systems/si/include/units/isq/si/acceleration.h

@@ -39,6 +39,8 @@ struct dim_acceleration : isq::dim_acceleration<dim_acceleration, metre_per_seco
 template<UnitOf<dim_acceleration> U, Representation Rep = double>
 using acceleration = quantity<dim_acceleration, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // m/s2
@@ -47,4 +49,6 @@ constexpr auto operator"" _q_m_per_s2(long double l) { return acceleration<metre
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/amount_of_substance.h

@@ -41,6 +41,8 @@ struct dim_amount_of_substance : isq::dim_amount_of_substance<mole> {};
 template<UnitOf<dim_amount_of_substance> U, Representation Rep = double>
 using amount_of_substance = quantity<dim_amount_of_substance, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // mol
@@ -49,6 +51,8 @@ constexpr auto operator"" _q_mol(long double l) { return amount_of_substance<mol
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto mol = reference<dim_amount_of_substance, mole>{};

src/systems/si/include/units/isq/si/angular_velocity.h

@@ -41,6 +41,8 @@ struct dim_angular_velocity : isq::dim_angular_velocity<dim_angular_velocity, ra
 template<UnitOf<dim_angular_velocity> U, Representation Rep = double>
 using angular_velocity = quantity<dim_angular_velocity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // rad / s
@@ -49,4 +51,6 @@ constexpr auto operator"" _q_rad_per_s(long double l) { return angular_velocity<
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/area.h

@@ -63,6 +63,8 @@ struct hectare : alias_unit<square_hectometre, "ha", no_prefix> {};
 template<UnitOf<dim_area> U, Representation Rep = double>
 using area = quantity<dim_area, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // m2
@@ -155,6 +157,8 @@ constexpr auto operator"" _q_ha(long double l) { return area<hectare, long doubl
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto m2 = reference<dim_area, square_metre>{};

src/systems/si/include/units/isq/si/capacitance.h

@@ -63,6 +63,8 @@ struct dim_capacitance : isq::dim_capacitance<dim_capacitance, farad, dim_electr
 template<UnitOf<dim_capacitance> U, Representation Rep = double>
 using capacitance = quantity<dim_capacitance, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // F
@@ -151,6 +153,8 @@ constexpr auto operator"" _q_YF(long double l) { return capacitance<yottafarad,
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto F = reference<dim_capacitance, farad>{};

src/systems/si/include/units/isq/si/catalytic_activity.h

@@ -65,6 +65,8 @@ struct dim_catalytic_activity : isq::dim_catalytic_activity<dim_catalytic_activi
 template<UnitOf<dim_catalytic_activity> U, Representation Rep = double>
 using catalytic_activity = quantity<dim_catalytic_activity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // kat
@@ -157,6 +159,8 @@ constexpr auto operator"" _q_U(long double l) { return catalytic_activity<enzyme
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto kat = reference<dim_catalytic_activity, katal>{};

src/systems/si/include/units/isq/si/charge_density.h

@@ -47,6 +47,8 @@ using charge_density = quantity<dim_charge_density, U, Rep>;
 template<UnitOf<dim_surface_charge_density> U, Representation Rep = double>
 using surface_charge_density = quantity<dim_surface_charge_density, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // C/m³
@@ -59,4 +61,6 @@ constexpr auto operator"" _q_C_per_m2(long double l) { return surface_charge_den
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/concentration.h

@@ -40,6 +40,8 @@ struct dim_concentration : isq::dim_concentration<dim_concentration, mol_per_met
 template<UnitOf<dim_concentration> U, Representation Rep = double>
 using concentration = quantity<dim_concentration, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // mol/m³
@@ -48,5 +50,7 @@ constexpr auto operator"" _q_mol_per_m3(long double l) { return concentration<mo
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si
 

src/systems/si/include/units/isq/si/conductance.h

@@ -58,6 +58,8 @@ struct dim_conductance : isq::dim_conductance<dim_conductance, siemens, dim_resi
 template<UnitOf<dim_conductance> U, Representation Rep = double>
 using conductance = quantity<dim_conductance, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // R
@@ -130,6 +132,8 @@ constexpr auto operator"" _q_YS(long double l) { return conductance<yottasiemens
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto S = reference<dim_conductance, siemens>{};

src/systems/si/include/units/isq/si/current_density.h

@@ -42,6 +42,8 @@ struct dim_current_density : isq::dim_current_density<dim_current_density, amper
 template<UnitOf<dim_current_density> U, Representation Rep = double>
 using current_density = quantity<dim_current_density, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // A / m²
@@ -50,4 +52,6 @@ constexpr auto operator"" _q_A_per_m2(long double l) { return current_density<am
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/density.h

@@ -42,6 +42,8 @@ struct dim_density : isq::dim_density<dim_density, kilogram_per_metre_cub, dim_m
 template<UnitOf<dim_density> U, Representation Rep = double>
 using density = quantity<dim_density, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // kg / m³
@@ -50,4 +52,6 @@ constexpr auto operator"" _q_kg_per_m3(long double l) { return density<kilogram_
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/dynamic_viscosity.h

@@ -40,6 +40,8 @@ struct dim_dynamic_viscosity : isq::dim_dynamic_viscosity<dim_dynamic_viscosity,
 template<UnitOf<dim_dynamic_viscosity> U, Representation Rep = double>
 using dynamic_viscosity = quantity<dim_dynamic_viscosity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Pa·s
@@ -48,5 +50,7 @@ constexpr auto operator"" _q_Pa_s(long double l) { return dynamic_viscosity<pasc
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si
 

src/systems/si/include/units/isq/si/electric_charge.h

@@ -42,6 +42,8 @@ struct dim_electric_charge : isq::dim_electric_charge<dim_electric_charge, coulo
 template<UnitOf<dim_electric_charge> U, Representation Rep = double>
 using electric_charge = quantity<dim_electric_charge, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // C
@@ -50,6 +52,8 @@ constexpr auto operator"" _q_C(long double l) { return electric_charge<coulomb,
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto C = reference<dim_electric_charge, coulomb>{};

src/systems/si/include/units/isq/si/electric_current.h

@@ -61,6 +61,8 @@ struct dim_electric_current : isq::dim_electric_current<ampere> {};
 template<UnitOf<dim_electric_current> U, Representation Rep = double>
 using electric_current = quantity<dim_electric_current, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // A
@@ -149,6 +151,8 @@ constexpr auto operator"" _q_YA(long double l) { return electric_current<yottaam
 
 } // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto A = reference<dim_electric_current, ampere>{};

src/systems/si/include/units/isq/si/electric_field_strength.h

@@ -39,6 +39,8 @@ struct dim_electric_field_strength : isq::dim_electric_field_strength<dim_electr
 template<UnitOf<dim_electric_field_strength> U, Representation Rep = double>
 using electric_field_strength = quantity<dim_electric_field_strength, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // V/m
@@ -47,4 +49,6 @@ constexpr auto operator"" _q_V_per_m(long double l) { return electric_field_stre
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/energy.h

@@ -61,6 +61,8 @@ struct dim_energy : isq::dim_energy<dim_energy, joule, dim_force, dim_length> {}
 template<UnitOf<dim_energy> U, Representation Rep = double>
 using energy = quantity<dim_energy, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // J
@@ -141,6 +143,8 @@ constexpr auto operator"" _q_GeV(long double l) { return energy<gigaelectronvolt
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto J = reference<dim_energy, joule>{};

src/systems/si/include/units/isq/si/energy_density.h

@@ -40,6 +40,8 @@ struct dim_energy_density : isq::dim_energy_density<dim_energy_density, joule_pe
 template<UnitOf<dim_energy_density> U, Representation Rep = double>
 using energy_density = quantity<dim_energy_density, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // N/m
@@ -48,4 +50,6 @@ constexpr auto operator"" _q_J_per_m3(long double l) { return energy_density<jou
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/force.h

@@ -63,6 +63,8 @@ struct dim_force : isq::dim_force<dim_force, newton, dim_mass, dim_acceleration>
 template<UnitOf<dim_force> U, Representation Rep = double>
 using force = quantity<dim_force, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // N
@@ -151,6 +153,8 @@ constexpr auto operator"" _q_YN(long double l) { return force<yottanewton, long
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto N = reference<dim_force, newton>{};

src/systems/si/include/units/isq/si/frequency.h

@@ -57,6 +57,8 @@ struct dim_frequency : isq::dim_frequency<dim_frequency, hertz, dim_time> {};
 template<UnitOf<dim_frequency> U, Representation Rep = double>
 using frequency = quantity<dim_frequency, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Hz
@@ -129,6 +131,8 @@ constexpr auto operator"" _q_YHz(long double l) { return frequency<yottahertz, l
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto Hz = reference<dim_frequency, hertz>{};

src/systems/si/include/units/isq/si/heat_capacity.h

@@ -53,6 +53,8 @@ using specific_heat_capacity = quantity<dim_specific_heat_capacity, U, Rep>;
 template<UnitOf<dim_molar_heat_capacity> U, Representation Rep = double>
 using molar_heat_capacity = quantity<dim_molar_heat_capacity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // J/K
@@ -69,5 +71,7 @@ constexpr auto operator"" _q_J_per_mol_K(long double l) { return molar_heat_capa
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si
 

src/systems/si/include/units/isq/si/inductance.h

@@ -59,6 +59,8 @@ struct dim_inductance : isq::dim_inductance<dim_inductance, henry, dim_magnetic_
 template<UnitOf<dim_inductance> U, Representation Rep = double>
 using inductance = quantity<dim_inductance, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // H
@@ -131,6 +133,8 @@ constexpr auto operator"" _q_YH(long double l) { return inductance<yottahenry, l
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto H = reference<dim_inductance, henry>{};

src/systems/si/include/units/isq/si/length.h

@@ -63,6 +63,8 @@ struct dim_length : isq::dim_length<metre> {};
 template<UnitOf<dim_length> U, Representation Rep = double>
 using length = quantity<dim_length, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // m
@@ -155,6 +157,8 @@ constexpr auto operator"" _q_au(long double l) { return length<astronomical_unit
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto m = reference<dim_length, metre>{};

src/systems/si/include/units/isq/si/luminance.h

@@ -40,6 +40,8 @@ struct dim_luminance : isq::dim_luminance<dim_luminance, candela_per_metre_sq, d
 template<UnitOf<dim_luminance> U, Representation Rep = double>
 using luminance = quantity<dim_luminance, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // cd/m²
@@ -48,5 +50,7 @@ constexpr auto operator"" _q_cd_per_m2(long double l) { return luminance<candela
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si
 

src/systems/si/include/units/isq/si/luminous_intensity.h

@@ -61,6 +61,8 @@ struct dim_luminous_intensity : isq::dim_luminous_intensity<candela> {};
 template<UnitOf<dim_luminous_intensity> U, Representation Rep = double>
 using luminous_intensity = quantity<dim_luminous_intensity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // cd
@@ -149,6 +151,8 @@ constexpr auto operator"" _q_Ycd(long double l) { return luminous_intensity<yott
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto cd = reference<dim_luminous_intensity, candela>{};

src/systems/si/include/units/isq/si/magnetic_flux.h

@@ -59,6 +59,8 @@ struct dim_magnetic_flux : isq::dim_magnetic_flux<dim_magnetic_flux, weber, dim_
 template<UnitOf<dim_magnetic_flux> U, Representation Rep = double>
 using magnetic_flux = quantity<dim_magnetic_flux, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Wb
@@ -131,6 +133,8 @@ constexpr auto operator"" _q_YWb(long double l) { return magnetic_flux<yottawebe
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto Wb = reference<dim_magnetic_flux, weber>{};

src/systems/si/include/units/isq/si/magnetic_induction.h

@@ -63,6 +63,8 @@ struct dim_magnetic_induction : isq::dim_magnetic_induction<dim_magnetic_inducti
 template<UnitOf<dim_magnetic_induction> U, Representation Rep = double>
 using magnetic_induction = quantity<dim_magnetic_induction, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // T
@@ -139,6 +141,8 @@ constexpr auto operator"" _q_G(long double l) { return magnetic_induction<gauss,
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto T = reference<dim_magnetic_induction, tesla>{};

src/systems/si/include/units/isq/si/mass.h

@@ -85,6 +85,8 @@ struct dim_mass : isq::dim_mass<kilogram> {};
 template<UnitOf<dim_mass> U, Representation Rep = double>
 using mass = quantity<dim_mass, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // g
@@ -261,6 +263,8 @@ constexpr auto operator"" _q_Da(long double l) { return mass<dalton, long double
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto g = reference<dim_mass, gram>{};

src/systems/si/include/units/isq/si/molar_energy.h

@@ -42,6 +42,8 @@ struct dim_molar_energy : isq::dim_molar_energy<dim_molar_energy, joule_per_mole
 template<UnitOf<dim_molar_energy> U, Representation Rep = double>
 using molar_energy = quantity<dim_molar_energy, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // J/mol
@@ -50,4 +52,6 @@ constexpr auto operator"" _q_J_per_mol(long double l) { return molar_energy<joul
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/momentum.h

@@ -40,6 +40,8 @@ struct dim_momentum : isq::dim_momentum<dim_momentum, kilogram_metre_per_second,
 template<UnitOf<dim_momentum> U, Representation Rep = double>
 using momentum = quantity<dim_momentum, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // kg*m/s
@@ -48,4 +50,6 @@ constexpr auto operator"" _q_kg_m_per_s(long double l) { return momentum<kilogra
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/permeability.h

@@ -41,6 +41,8 @@ struct dim_permeability : isq::dim_permeability<dim_permeability, henry_per_metr
 template<UnitOf<dim_permeability> U, Representation Rep = double>
 using permeability = quantity<dim_permeability, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // H/m
@@ -49,5 +51,7 @@ constexpr auto operator"" _q_H_per_m(long double l) { return permeability<henry_
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si
 

src/systems/si/include/units/isq/si/permittivity.h

@@ -41,6 +41,8 @@ struct dim_permittivity : isq::dim_permittivity<dim_permittivity, farad_per_metr
 template<UnitOf<dim_permittivity> U, Representation Rep = double>
 using permittivity = quantity<dim_permittivity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // F/m
@@ -49,5 +51,7 @@ constexpr auto operator"" _q_F_per_m(long double l) { return permittivity<farad_
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si
 

src/systems/si/include/units/isq/si/power.h

@@ -58,6 +58,8 @@ struct dim_power : isq::dim_power<dim_power, watt, dim_energy, dim_time> {};
 template<UnitOf<dim_power> U, Representation Rep = double>
 using power = quantity<dim_power, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // W
@@ -130,6 +132,8 @@ constexpr auto operator"" _q_YW(long double l) { return power<yottawatt, long do
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto W = reference<dim_power, watt>{};

src/systems/si/include/units/isq/si/pressure.h

@@ -63,6 +63,8 @@ struct dim_pressure : isq::dim_pressure<dim_pressure, pascal, dim_force, dim_are
 template<UnitOf<dim_pressure> U, Representation Rep = double>
 using pressure = quantity<dim_pressure, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Pa
@@ -151,6 +153,8 @@ constexpr auto operator"" _q_YPa(long double l) { return pressure<yottapascal, l
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto Pa = reference<dim_pressure, pascal>{};

src/systems/si/include/units/isq/si/radioactivity.h

@@ -61,6 +61,8 @@ struct dim_radioactivity : isq::dim_radioactivity<dim_radioactivity, becquerel,
 template<UnitOf<dim_radioactivity> U, Representation Rep = double>
 using radioactivity = quantity<dim_radioactivity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Bq
@@ -149,6 +151,8 @@ constexpr auto operator"" _q_YBq(long double l) { return radioactivity<yottabecq
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto Bq = reference<dim_radioactivity, becquerel>{};

src/systems/si/include/units/isq/si/resistance.h

@@ -59,6 +59,8 @@ struct dim_resistance : isq::dim_resistance<dim_resistance, ohm, dim_voltage, di
 template<UnitOf<dim_resistance> U, Representation Rep = double>
 using resistance = quantity<dim_resistance, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // R
@@ -131,6 +133,8 @@ constexpr auto operator"" _q_YR(long double l) { return resistance<yottaohm, lon
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto R = reference<dim_resistance, ohm>{};

src/systems/si/include/units/isq/si/speed.h

@@ -42,6 +42,8 @@ struct kilometre_per_hour : deduced_unit<kilometre_per_hour, dim_speed, kilometr
 template<UnitOf<dim_speed> U, Representation Rep = double>
 using speed = quantity<dim_speed, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // m/s
@@ -54,4 +56,6 @@ constexpr auto operator"" _q_km_per_h(long double l) { return speed<kilometre_pe
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/surface_tension.h

@@ -40,6 +40,8 @@ struct dim_surface_tension : isq::dim_surface_tension<dim_surface_tension, newto
 template<UnitOf<dim_surface_tension> U, Representation Rep = double>
 using surface_tension = quantity<dim_surface_tension, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // N/m
@@ -48,4 +50,6 @@ constexpr auto operator"" _q_N_per_m(long double l) { return surface_tension<new
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/thermal_conductivity.h

@@ -41,6 +41,8 @@ struct dim_thermal_conductivity : isq::dim_thermal_conductivity<dim_thermal_cond
 template<UnitOf<dim_thermal_conductivity> U, Representation Rep = double>
 using thermal_conductivity = quantity<dim_thermal_conductivity, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // W/(m K)
@@ -49,4 +51,6 @@ constexpr auto operator"" _q_W_per_m_K(long double l) { return thermal_conductiv
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/thermodynamic_temperature.h

@@ -40,6 +40,8 @@ struct dim_thermodynamic_temperature : isq::dim_thermodynamic_temperature<kelvin
 template<UnitOf<dim_thermodynamic_temperature> U, Representation Rep = double>
 using thermodynamic_temperature = quantity<dim_thermodynamic_temperature, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // K
@@ -48,6 +50,8 @@ constexpr auto operator"" _q_K(long double l) { return thermodynamic_temperature
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto K = reference<dim_thermodynamic_temperature, kelvin>{};

src/systems/si/include/units/isq/si/time.h

@@ -52,6 +52,8 @@ struct dim_time : isq::dim_time<second> {};
 template<UnitOf<dim_time> U, Representation Rep = double>
 using time = quantity<dim_time, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // ys
@@ -104,6 +106,8 @@ constexpr auto operator"" _q_d(long double l) { return time<day, long double>(l)
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto ys = reference<dim_time, yoctosecond>{};

src/systems/si/include/units/isq/si/torque.h

@@ -42,6 +42,8 @@ struct dim_torque : isq::dim_torque<dim_torque, newton_metre_per_radian, dim_for
 template<UnitOf<dim_torque> U, Representation Rep = double>
 using torque = quantity<dim_torque, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // Nm
@@ -50,4 +52,6 @@ constexpr auto operator"" _q_Nm_per_rad(long double l) { return torque<newton_me
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 }  // namespace units::isq::si

src/systems/si/include/units/isq/si/voltage.h

@@ -63,6 +63,8 @@ struct dim_voltage : isq::dim_voltage<dim_voltage, volt, dim_power, dim_electric
 template<UnitOf<dim_voltage> U, Representation Rep = double>
 using voltage = quantity<dim_voltage, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // V
@@ -151,6 +153,8 @@ constexpr auto operator"" _q_YV(long double l) { return voltage<yottavolt, long
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto V = reference<dim_voltage, volt>{};

src/systems/si/include/units/isq/si/volume.h

@@ -83,6 +83,8 @@ struct yottalitre : prefixed_unit<yottalitre, yotta, litre> {};
 template<UnitOf<dim_volume> U, Representation Rep = double>
 using volume = quantity<dim_volume, U, Rep>;
 
+#if UNITS_UDLS
+
 inline namespace literals {
 
 // m3
@@ -255,6 +257,8 @@ constexpr auto operator"" _q_Yl(long double l) { return volume<yottalitre, long
 
 }  // namespace literals
 
+#endif // UNITS_UDLS
+
 namespace references {
 
 inline constexpr auto m3 = reference<dim_volume, cubic_metre>{};