# Release Notes

## mp-units

### 2.5.0 <small>WIP</small> { id="2.5.0" }

- (!) feat: representation concepts improved
- (!) feat: `representation_of` concept now also accepts a `quantity_spec` and accepts any representation character for quantity kinds
- (!) feat: `quantity::one()` removed
- (!) feat: `Representation` concept removed
- feat: `SymbolicArg` applied to expression templates
- feat: `per` and `power` made `final`
- feat: `derived_XXX` are now constrained with `SymbolicConstant`
- feat: prime factorization extended to any magnitude (thanks [@chiphogg](https://github.com/chiphogg))
- feat: `cartesian_vector` added
- feat: `equivalent` now accept any units (even non-convertible)
- feat: text output should fallback to the portable mode when UTF-8 is not used for `text_encoding`
- feat: precondition added to `to_u8string`
- feat: text output of scaled units is now enclosed in parenthesis `(...)` instead of brackets `[...]`
- feat: `abs(quantity)` exposed for conforming freestanding implementations
- feat: proper constraints for `kind_of`
- feat: missing precondition added for `quantity::op/`
- feat: `quantity_spec` conversions improved
- feat: `rankine` unit added
- feat: `std::numeric_limits` support added
- feat: `scaling_overflows_non_zero_values` added to detect conversions overflowing `rep`
- feat: deprecation messages now provide the release version where the deprecation happened
- feat: electromagnetism.h updated to IEC80000-6-2022
- feat: `ConvertibleWithNumber` introduced to improve convertibility of unit `one` with raw numbers
- feat: `lerp` and `midpoint` for points added
- feat: `is_value_preserving` customization point added
- feat(example): `is_vector` specialization no longer needed for `si_constants`
- (!) refactor: `type_list` moved to implementation details
- (!) refactor: from now `unit_symbol` and `dimension_symbol` always returns `std::string_view`
- (!) refactor: `text_encoding` renamed to `character_set`
- (!) refactor: `Magnitude` renamed to `UnitMagnitude` and `magnitude` to `unit_magnitude`
- (!) refactor: `unit_magnitude` moved to `detail` namespace
- (!) refactor: `absolute` renamed to `point`
- (!) refactor: `power` members refactored to be explicitly exposition only
- (!) refactor: `is_XXX` customization points for representation types removed
- (!) refactor: `quantity_values` renamed to representation values
- (!) refactor: `scalar` and `complex` characters renamed to `real_scalar` and `complex_scalar` respectively + concepts refactoring
- (!) refactor: `MagConstant` concept renamed to `detail::is_mag_constant` variable trait
- refactor: mp_units.core defined in terms of `core.h`
- refactor: `MP_UNITS_NONCONST_TYPE` introduced to benefit from the C++23 feature
- refactor: `SymbolicConstant` concept refactored
- refactor: explicit type of `op/` for `quantity` and `reference` replaced with constrained placeholder
- refactor: private `unit_magnitude` interface renamed to not use leading `_`
- refactor: `one_of` concept removed and replaced with `QSProperty` in `quantity_spec`
- refactor: `std::is_trivial` will be deprecated in C++26
- refactor: `SameQuantitySpec` concept removed and replaced with direct comparison
- refactor: unused `SameReference` concept removed
- refactor: `type_name_less` introduced and used as a default predicate for expression templates
- refactor: "expression templates" renamed to "symbolic expressions"
- refactor: `all_are_kinds` removed and `get_associated_quantity` simplified
- refactor: `reference` now returns explicit types for `inverse`, `pow`, `sqrt`, and `cbrt`
- refactor: repeated concept checks removed from `get_common_reference`
- refactor: `std::assignable_from` used in `ValuePreservingTo` concept
- refactor: `quantity` constructor refactored to use another constructor with the result of `sudo_cast`
- refactor: preconditions for quantity operations now use `is_neq_zero`
- refactor: implicit expression variations used in `quantity` and `quantity_point` constraints
- refactor: `inverse()` constraints improved
- refactor: `make_quantity_point` introduced
- refactor: `point_origin_interface::op+` return type unified with the rest of the interfaces
- refactor: `std::convertible_to` replaced with `std::same_as` in `basic_fixed_string`
- refactor: `less`, `ceil`, and `round` refactored and improved + more unit tests for `round`
- refactor: `math_concepts.h` removed and concepts replaced with explicit expression in constraints
- refactor: `visit_format_arg` is deprecated in C++26
- refactor: deprecated literal operators
- refactor: constraints refactoring
- (!) fix: `electric_current_phasor`, `voltage_phasor`, `apparent_power` switched to complex character
- (!) fix: `position_vector` and `displacement` moved to a different place in a tree
- (!) fix: `velocity` is now defined in terms of `displacement` instead of `position_vector`
- fix: missing `core.h` added to CMake
- fix: `const` was leaking to some `SymbolicConstant`s
- fix: `make_reference` should skip only the exact kinds deduced from a unit
- fix: inconsistencies in `get_common_quantity_spec()` fixed
- fix: unused `convertible_kinds()` argument removed
- fix: compile-time branch condition fixed in `quantity_point::point_for`
- fix: `inverse(Quantity)` fixed for subkinds of `dimensionless`
- fix: `point_origin_interface::op+` constraints fixed
- fix: missing `get_common_unit()` overload added
- fix: `floor` and `ceil` constraints fixed
- fix: quantity characters fixed in electromagnetism quantities
- fix: `arg.visit` support fixed
- fix: `expr_less` now also sorts powers
- fix: `mag_constant` workarounds branches for clang fixed
- fix: checking for clang versions fixed in CMake scripts
- fix: text stripping in `type_name` fixed
- test: lots of tests for complex quantities
- test: runtime unit tests refactored to have a bigger granularity (less top level tests)
- test: _surface tension_ replaced with _entropy_ in an fmt test
- test: test_package now is tested also with C++20 modules
- test: tests for dimensionless quantities static data members
- test: a few more natural units tests added
- test: tests to check if `quantity` satisfies `Scalar`
- test: add static tests for concept `DimensionOf` (thanks [@jvocht](https://github.com/jvocht))
- test: quantity character concepts tests for quantities added
- docs: ISQ part 6 released
- docs: new chapter about our documentation added to the contributing guide
- docs: directory name updated in the contributing guide
- docs: mp-units Conan options added to conanfile.txt examples
- docs: `contracts` Conan option default value description improved
- docs: outdated note removed from the "Text Output" chapter
- docs: a paragraph about additional formatting options removed (applicable only to quantity symbols which we do not support)
- docs: Wrocław 2024 meeting report
- docs: explicit unit conversion example added to the "Symbols of common units" chapter
- docs: "Bringing Quantity-Safety To The Next Level" blog post added
- docs: quantity-safety mentioned in the docs
- docs: `complex` character added to the "Quantity character" chapter
- docs: intro to "Value Conversions" chapter added
- docs: "Scaling overflow prevention" chapter added
- docs: "Concepts" chapter updated
- docs: old customization points removed from the "Character of a Quantity" chapter
- docs: clang-19 issues mentioned in a compiler support table
- docs(ref): document most of `mp_units.core` (thanks [@JohelEGP](https://github.com/JohelEGP))
- build: `CheckCacheVarValues` CMake module file added
- build: `MP_UNITS_DEV_TIME_TRACE` CMake option added
- build: `MP_UNITS_API_NO_CRTP` removed from `test_package` CMake
- build: require at least CMake 3.31 with Conan
- build: clang-20 enabled in CI
- build: clang-19 support removed from conanfile.py
- build: clang-20.1 workaround added to `package_info`
- build: update dependencies to gsl-lite/0.42.0, ms-gsl/4.1.0, fmt/11.1.4, and catch2/3.8.0
- build: suppress warnings for gcc-12 in conanfile
- ci: CI matrix generation added (thanks [@burnpanck](https://github.com/burnpanck))
- ci: `import_std` now checks if at least C++23 is being used
- perf: caching of the results of heavy `consteval` functions execution added
- perf: `expr_projectable` concept removed to improve compilation performance

### 2.4.0 <small>November 5, 2024</small> { id="2.4.0" }

- (!) feat: `phase_velocity` and `group_velocity` aliases removed from ISQ by ISO
- feat: `iec::bit` using-declared in `iec::unit_symbols`
- feat: common unit symbols now use `EQUIV{u1, u2, ...}` syntax
- feat: `scaled_unit` symbol printing improved (`[]` around the entire unit, small magnitude values do not use a power of `10` anymore)
- feat: `scaled_unit` does not have a priority over `derived_unit` anymore
- feat: fractional exponents support added to `mag_power`
- feat: tag types are now required to be empty
- feat: magnitude text now obeys formatting parameters and knows how to print constants
- feat: added support for printing powers of magnitude constants
- feat: `SymbolicConstant` concept added
- feat: `common_unit` selection algorithm improved to make `rev + rad` return `rad`
- feat: litre text symbol changed from `l` to `L` to avoid ambiguity with `1`
- feat: alternative litre unit symbol `L` added to prevent ambiguities with `1`
- feat: Unicode unit symbols
- feat: `π` added as an alias for `pi`
- feat: `expr_pow` extended to remove redundancy in callers
- feat: `DerivedDimensionExpr`, `DerivedQuantitySpecExpr` and `DerivedUnitExpr` removed
- feat: `MagnitudeSpecExpr` and `PowerVBase` removed and some functions renamed to limit possible ambiguity in overload resolution
- feat: `std::is_object` constraint applied to `value_type_t`
- feat: `quantity_values` are now defined on top of `std::chrono::duration_values`
- feat: from now on truncation is not allowed in compound assignment
- feat(example): currency example now uses `chrono::time_point` and has better interfaces
- feat(example): `treat_as_floating_point` specializations for examples' types removed
- (!) refactor: all `iec` quantity specifications are now deprecated and moved to `isq`
- (!) refactor: `mag_constant` now takes a symbol and a value and the class deriving from it must be final
- (!) refactor: `op==(U1, U2)` now checks for the same type (old behavior available as `equivalent(U1, U2)`) + `convertible` now verifies associated `quantity_spec` as well
- (!) refactor: `ascii` -> `portable`, `unicode` -> `utf8`, 'A' -> 'P'
- (!) refactor: `char_traits` removed from `fixed_string`
- (!) refactor: convertibility traits and concepts refactored to use `bool` flags instead of wrappers
- (!) refactor: tag types should not expose their members
- refactor: `convertible(U1, U2)` implementation simplified
- refactor: `abs` moved to `constexpr_math.h`
- refactor: `unit_symbol_impl` simplified
- refactor: `unit_symbol_formatting` moved to a dedicated header file
- refactor: `shorten_T` removed
- refactor: magnitude interface cleanup
- refactor: `derived_from_the_same_base_dimension` no longer needed
- refactor: `one_of` usage removed from the `fixed_string` deduction guides
- refactor: `quantity.h` is not needed in `constants.h` (`unit.h` is enough)
- refactor: `SameDimension` concept is not needed and can be inlined in `DimensionOf`
- refactor: framework Unicode symbols are now spelled using their codes
- refactor: `QuantitySpecWithNoSpecifiers` removed and `kind_of` definition simplified
- refactor: `treat_as_floating_point` simplified and extended to use `std::chrono::treat_as_floating_point_v`
- refactor: `wrapped_type_t` reuses `std::indirectly_readable_traits`
- refactor: `expr_fractions` takes direct `OneType` type now instead of a trait
- refactor: Unicode symbols description reworked based on the latest SG16 recommendations
- refactor: `Mutable` concept applied to `quantity` and `quantity_point`
- refactor: `explicit` cleanup for deduction guides of `quantity` and `quantity_point`
- refactor: `point_origin_interface::op-` cleanup
- refactor: `QuantityLikeImpl` refactored to conform to API Reference by @JohelEGP
- refactor: `get_complexity` refactored to be 0-based and not account for a number of arguments in a list
- refactor: `get_complexity` refactored to returned maximum complexity of an element (instead of the sum of elements)
- refactor(test): `derived_quantity` refactored to `child_quantity`
- fix: missing `are_ingredients_convertible` overloads added
- fix: constraints for magnitude added for `scaled_unit` and fixed `common_unit` instantiating it incorrectly
- fix: according to ISO 80000-16 `%` should always be prefixed with space
- fix: extraneous space in unit symbol having only denominators removed
- fix: explicit cast added to `less` for magnitudes to fix clang-arm64 conversion error
- fix: `common_unit` handling fixed for some corner cases
- fix: math functions constraints fixed
- fix: `operator*(M, U u)` fixed for `U` being `scaled_unit`
- fix: subsumption of `QuantityKindSpec` fixed
- fix: `ValuePreservingTo` fixed to apply `std::remove_cvref_t` on `FromRep`
- fix: compound assignment operations on quantities now behave the same as on the underlying representation types
- fix: `QuantityConvertibleTo` used in `quantity_point` compound assignment
- fix: `convertible_kinds` implementation fixed
- fix(tests): freestanding build fixed
- test: unit tests for the inverse of `mag_constant` added
- test: Unicode symbols used in unit tests
- test: more `std::chrono` tests added
- test: commutativity tests added to ISQ
- test: one `kind_of` test added to reference tests
- test: `pow<0>` and `pow<1>` tests added for dimensions
- test: more `get_common_quantity_spec` tests added
- build: setting of some test_package CMake options enabled only for a `cxx_modules` build
- ci: `sudo apt update` added for documentation.yml in hope that it will resolve missing system packages issue
- ci: MSVC added to the CI
- ci: the latest not-released docs will use "HEAD" as a version from now on
- ci: documentation action should run on a new tag as well
- ci: documentation action limited only to commits that change documentation files
- ci: non-documentation actions should not run on tags
- docs: missing systems added to the "Project Structure" chapter
- docs: graphs of ISQ kind hierarchies improved
- docs: category of the ISO meeting reports changed to "WG21 Updates"
- docs: blog comments support added
- docs: Part 1-5 articles of the ISQ series added
- docs: "Symbols of scaled units" chapter added + minor updates to scaled and common units chapters
- docs: conan profile updated to present gcc-14 instead of gcc-12 which is no longer supported
- docs: "Why derived units order is not preserved from the multiplication?" chapter added to FAQ
- docs: "Many shades of the same unit" extended with a note about the derived units order
- docs: API Reference now presents _index.html_ instead of _full.hml_

### 2.3.0 <small>September 27, 2024</small> { id="2.3.0" }

- (!) feat: `delta` and `absolute` construction helpers
- (!) feat: Conan and CMake options changed as requested at ConanCenter code review
- (!) feat: `unit_can_be_prefixed` removed - from now on all named units can be prefixed
- feat: formatting functions for units and dimensions marked as `constexpr` to enable compile-time text formatting
- feat: `qp1.quantity_from(qp2)` added
- feat: non-member `swap` added for `fixed_string`
- feat: simplified `inplace_vector` added
- feat: text output for angular units improved (space before symbol removed)
- feat: representation type template parameter added to value conversion functions
- feat: all tags in the expression templates are now ordered by the type names
- feat: convertibility of a quantity with a unit `one` with the raw value added
- feat: `import std;` support added
- feat: compute values for rational magnitude powers (thanks [@chiphogg](https://github.com/chiphogg))
- feat: `value_cast<Representation, Unit>()` complementary conversion function added
- feat: `hw_voltage` example added
- feat: `MP_UNITS_IMPORT_STD` and `MP_UNITS_MODULES` handled properly in `test_package.cpp`
- feat: `complex` quantity character added
- feat: `iec::var` unit added
- feat: `type_list_unique` added
- feat: `for_each` on `std::tuple` added
- feat: `common_unit` support added
- (!) refactor: `quantity_point_like_traits` now use numerical value instead of the quantity
- (!) refactor: `iec80000` system renamed to `iec`
- (!) refactor: `mag_pi` is now `mag<pi>`
- (!) refactor: `common_XXX()` functions renamed to `get_common_XXX()`
- refactor: error messages-related improvements
- refactor: `[[nodiscard]]` and `consteval` set for some magnitude-related functions
- refactor: degree Celsius and Fahrenheit symbols text now use Unicode codepoints
- refactor: `dimension_symbol` and `units_symbol` refactored to use `inplace_vector`
- refactor: `unit_symbol` and `dimension_symbol` refactored for readability and `consteval`
- refactor: binary operators of `quantity` and `quantity_point` are now hidden friends
- refactor: tag types-related operators are now hidden friends as well
- refactor: `ValuePreservingTo` concept added
- refactor: perfect forwarding interfaces improved
- refactor: `Representation` concepts now requires `WeaklyRegular` instead of `std::regular`
- refactor: `quantity_point` default-constructibility removed from the `quantity_from` constraints
- refactor: `has_common_type_v` simplified
- refactor: `is_power_of_quantity_spec` and `is_power_of_dim` variable templates converted to concepts
- refactor: unnecessary custom versions of `is_specialization_of` removed
- refactor: `is_derived_from_specialization_of_v` added and applied to remove custom traits
- fix: signatures of capacity functions of `fixed_string` fixed
- fix: `MP_UNITS_API_NO_CRTP` handling fixed
- fix: `MP_UNITS_HOSTED` branch added to `core.h`
- fix: mkdocs dependencies fixed in the gitpod dockerfile
- fix: `MP_UNITS_API_CONTRACTS` should have a priority over headers availability
- fix: `si.h` and `angular.h` now properly include `hacks.h` to define `MP_UNITS_HOSTED` before its usage
- fix: quantity scaling between different prefixes improved
- fix: conversion operator to `std::chrono` types fixed
- fix: `std::format` does not always use `Char*` as iterators
- fix: `complex_power` & co fixed
- fix: `__cpp_deleted_function` workaround for clang-19 added
- test: conversion to chrono unit tests added
- test: unit tests for creating a quantity from a `volatile` variable
- test: increase tolerance for certain math tests to two epsilon by [@burnpanck](https://github.com/burnpanck)
- test: `std::complex`-based quantities tests added
- build: conanfile bumped to use `catch2/3.7.0`
- build: conanfile bumped to use `fmt/11.0.1`
- build: minimum required CMake version bumped to 3.25
- build: duplicated `cmake_minimum_required` commands removed
- build: minimum conan version set to 2.0.15
- build: MSVC compilation enabled for the library part by [@czjhoppe](https://github.com/czjhoppe)
- build: Dockerfile updated for gitpod
- build: `generate()` in `test_package` now correctly propagates project's options
- build: `target_include_directories` is not needed anymore
- build: `target_compile_features` now uses `CMAKE_CXX_STANDARD`
- build: `package_type` is dynamically set in conanfile.py depending if we build modules or not
- build(conan): packaging improved
- ci: added test for upstream clang on macos-14, as an example for an arm64 platform by [@burnpanck](https://github.com/burnpanck)
- style: pre-commit updated to clang-format-18.1.8
- docs: "Strong Angular System" chapter added
- docs: docs updated to use new spelling for Conan options
- docs: "Interface Introduction" chapter updated
- docs: St. Louis 2024 report added
- docs: "Radians and degrees support" added
- docs: Rework of "Getting Started" section
- docs: "API Reference" support added (thanks [@JohelEGP](https://github.com/JohelEGP))
- docs: "Generating API reference" chapter added
- docs: minor formatting and spelling improvements to the "CONTRIBUTING.md"
- docs: "Unit symbols" chapter added
- docs: examples line numbers fixed
- docs: "Text Formatting" tag removed from avg_speed example
- docs: line breaks in mermaid graphs fixed
- docs: 2.3.0 release added

### 2.2.1 <small>July 3, 2024</small> { id="2.2.1" }

- (!) feat: Conan and CMake options refactored

### 2.2.0 <small>June 14, 2024</small> { id="2.2.0" }

- (!) feat: C++ modules support added by [@JohelEGP](https://github.com/JohelEGP)
- (!) feat: New formatting specification implemented
- (!) feat: `has_unit_symbol` support removed
- (!) feat: ABI concerns resolved with introduction of u8 strings for symbols
- (!) feat: API-related Conan, CMake, and preprocessor options redesigned
- (!) feat: `core.h` removed
- (!) feat: from now on units, dimensions, quantity specifications, and point origins have to be marked as `final`
- feat: implicit point origins support added
- feat: unit default point origin support added
- feat: `fma`, `isfinite`, `isinf`, and `isnan` math function added by [@NAThompson](https://github.com/NAThompson)
- feat: `fma` for quantity points added
- feat: `quantity_point` support added for `quantity_cast` and `value_cast`
- feat: `value_cast<Unit, Representation>` added
- feat: `value_cast<Quantity>(q)`, `value_cast<Quantity>(qp)` and `value_cast<QuantityPoint>(qp)` added by [@burnpanck](https://github.com/burnpanck)
- feat: `interconvertible(quantity_spec, quantity_spec)` added
- feat: `qp.quantity_from_zero()` added
- feat: `value_type` type trait added
- feat: do not print space between a number and `percent` or `per_mille`
- feat: `ppm` parts per million added by [@nebkat](https://github.com/nebkat)
- feat: `atan2` 2-argument arctangent added by [@nebkat](https://github.com/nebkat)
- feat: `fmod` floating-point division remainder added by [@nebkat](https://github.com/nebkat)
- feat: `remainder` IEEE division remainder added by [@nebkat](https://github.com/nebkat)
- feat: `std::format` support added
- feat: unit text output support added
- feat: formatting error messages improved
- feat: improve types readability by eliminating extraneous `()` in references, prefixes, and `kind_of`
- feat: dimension and unit text output added
- feat: some light and radiation ISQ quantities added
- feat: allow configuring GSL library use
- feat: freestanding support added
- (!) refactor: `zero_Fahrenheit` renamed to `zeroth_degree_Fahrenheit`
- (!) refactor: SI-related trigonometric functions moved to the `si` subnamespace
- (!) refactor: `math.h` header file broke up to smaller pieces
- (!) refactor: `fixed_string` interface refactored
- (!) refactor: `ReferenceOf` does not take a dimension anymore
- (!) refactor: 'o' replaced with '1' as a modifier for `unit_symbol_solidus::one_denominator`
- (!) refactor: `get_kind()` now returns `kind_of`
- (!) refactor: FMT macros moved to `compat_macros.h`
- (!) refactor: `fixed_string` refactored to reflect the latest changes to [P3094R2](https://wg21.link/P3094R2)
- (!) refactor: `basic_symbol_text` renamed to `symbol_text`
- (!) refactor: `ratio` hidden as an implementation detail behind `mag_ratio`
- (!) refactor: `framework.h` introduced
- (!) refactor: type list tools made an implementation detail of the library
- (!) refactor: header files with the entire system definitions moved up in the directory tree
- (!) refactor: `absolute_point_origin` does not use CRTP anymore
- refactor: system's units do not inherit from one another anymore
- refactor: all units made `final`
- refactor: math functions constraints refactored
- refactor: `si_quantities.h` added to improve compile-times
- refactor: `validate_ascii_string` refactored to `is_basic_literal_character_set`
- refactor: `underlying_type` split to `wrapped_type` and `value_type` and used in code
- refactor: code refactored to comply with clang-tidy
- refactor: remove dependency on `<ranges>` header and switch to use an iterator-based `copy` algorithm
- refactor: `terminate` replaced with `abort` and a header file added
- refactor: most `std::remove_const_t` removed and some replaced with the GCC-specific workaround
- refactor: not needed `remove_reference_t` and `remove_cvref_t` removed
- refactor: binary operators of `quantity` and `quantity_point` are now hidden friends
- fix: `QuantityLike` conversions required `Q::rep` instead of using one provided by `quantity_like_traits`
- fix: `quantity_spec[Unit]` replaced with `make_reference` in `value_cast`
- fix: `ice_point` is now defined with the integral offset from `absolute_zero`
- fix: performance regression in `sudo_cast` fixed
- fix: explicit object parameter support fixed
- fix: missing `version` header file added to `hacks.h`
- fix: `quantity_cast` to accept lvalue references (thanks [@burnpanck](https://github.com/burnpanck))
- fix: `value_cast` with lvalue references to `quantity_point` (thanks [@burnpanck](https://github.com/burnpanck))
- docs: project blog and first posts added
- docs: project documentation layout refactored
- docs: "Interoperability with Other Libraries" chapter added
- docs: "Framework Basics" chapters updated and cleaned up
- docs: `smoot` unit example added to the main page
- docs: "Code Example" chapter renamed to "Look and Feel" and reordered in TOC to be after "Quick Start"
- docs: "Quick Start" chapter reworked to be simpler and include quantity points
- docs: "Quantity points" chapter extended
- docs: "The Affine Space" chapter updated to reflect the recent design changes
- docs: "Working with Legacy interfaces" chapter added
- docs: "Text Output" chapter updated
- docs: mkdocs social plugin enabled
- docs: project logo and custom color scheme added
- docs: minimum compiler requirements updated
- docs: unit symbols admonition extended in the "Quick Start" chapter
- docs: Cairo dependency described in the MkDocs section
- docs: "hello units" example updated with dimensions output
- docs: "Text Output" chapter updated with the recent formatting changes
- docs: formatting grammar language changed to EBNF
- docs: "Project structure" chapter expanded
- docs: CITATION.cff updated
- (!) build: Conan and CMake options refactored
- (!) build: `MP_UNITS_AS_SYSTEM_HEADERS` renamed to `MP_UNITS_BUILD_AS_SYSTEM_HEADERS`
- (!) build: `MP_UNITS_BUILD_LA` and `MP_UNITS_IWYU` CMake options now have `_DEV_` in the name
- build: gsl-lite updated to 0.41.0
- build: catch2 updated to 3.5.1
- build: fmt updated to 10.2.1
- build: gitpod environment updated
- build: `check_cxx_feature_supported` added
- build: IWYU path handling fixed
- build: IWYU enabled on GCC
- build: `CMAKE_EXPORT_COMPILE_COMMANDS` flag enabled for the developer's build
- build(conan): `generate()` now set `cache_variables`
- build(conan): `can_run` check added before running tests
- ci: Conan and CMake CI now use different cache names
- ci: gcc-14 added
- ci: `clang-tidy` CI added

### 2.1.1 <small>May 16, 2024</small> { id="2.1.1" }

- fix: unit tests compilation on gcc-14 fixed
- fix: explicit `this` parameter support fixed

### 2.1.0 <small>December 9, 2023</small> { id="2.1.0" }

- (!) feat: `inverse()` support added for dimensions, quantity_spec, units, and references
            (`1 / s` will now create `quantity` and not a `Unit`)
- (!) feat: `quantity_point` does not provide `zero()` anymore
- (!) feat: `quantity_spec` and its kind should not compare equal
- (!) feat: mutating interface removed from `fixed_string`
- (!) feat: `common_type` with a raw value is not needed anymore as for a long time now raw values are
  not convertible to the dimensionless quantities
- (!) feat: `symbol_text` definition simplified
- (!) feat: users are now allowed to inherit their own types from absolute point origins
- (!) feat: interoperability with other libraries redesigned
- feat: `basic_fixed_string(const CharT*, std::integral_constant<std::size_t, N>)` constructor added
- feat: `isq::activity` added and `becquerel` definition updated to benefit from it
- feat: `gray` and `sievert` now have correct associated quantity kinds
- feat: `UnitCompatibleWith` concept added and applied to `in(U)` and `force_in(U)` functions
- feat: quantities can now be multiplied and divided by units (no parenthesis needed anymore)
- feat: `Magnitude / Unit` operator added
- feat: equality for dimensions now will allow derived classes as well (but not from `derived_dimension`)
- feat: `zero_Fahrenheit` point origin added
- feat: equivalent point origins handling improved
- feat(example): unit symbols added to the currency example
- (!) refactor: `unit_symbol<fmt>(U)` signature refactored and the resulting text can now also be used at runtime
- (!) refactor: `make_xxx` factory functions replaced with two-parameter constructors
- (!) refactor: `unit_symbol` changed to `consteval`
- refactor: `in(U)` and `force_in(U)` now return `auto` to provide better diagnostics on clang
- refactor: `quantity` operators constraints refactored
- refactor: more type members added to `fixed_string` definition
- refactor: `unit_symbol_formatting` enums now use `std::int8_t` as a representation type
- fix: symbols of named dimensionless units with the ratio = 1 were not printed
- fix: iterator is now properly updated for all cases in `unit_symbol`
- fix: Fahrenheit conversion ratio was inverted
- fix: `CommonlyInvocableQuantities` was overconstrained for the current library design
- fix: `are_ingredients_convertible` now mandates explicit conversion for `To` dimensionless quantities
- fix: `quantity_point::point_for(PO)` constraints fixed
- fix(example): `latitude` and `longitude` fixed to include `0` for `N` and `E` respectively
- ci: clang-17 enabled
- ci: apple-clang-15 enabled
- ci: Added C++23 builds to the CI matrix
- docs: "Getting Started" chapters updated
- docs: "Basic Concepts" and "Interface Introduction" chapters updated
- docs: "Design Overview" chapter added and "Concepts" chapter reworked
- docs: "Output stream formatting" chapter updated
- docs: "Default formatting" chapter updated
- docs: "Derived unit symbols generation" chapter added
- docs: outdated affine space chapter updated
- docs: `CameCase` concept identifiers FAQ added
- docs: `gravitational_potential_energy` equation fixed on a graph
- docs: YouTube video link updated to the C++ on Sea 2023
- docs: ISO papers reference added to docs and README
- docs: a representation type in a dimensionless quantity FAQ fixed
- docs: titles added to some important admonitions
- docs: "Terms and Definitions" slightly updated
- docs: "canonical unit" added to glossary and its documentation in code was updated
- docs: Design overview graph updated

### 2.0.0 <small>September 24, 2023</small> { id="2.0.0" }

- `units` namespace renamed to `mp_units` (#317)
- header files in the `<mp-units/...>` rather then in `<units/...>` (#317)
- the downcasting facility is removed (#383, #211, #32)
- unified and simplified quantity creation (#274)
- determining the best way to create a quantity (#413)
- V2 `quantity_point` (#414)
- introduction of `quantity_spec` to store not only `dimension` but also additional information about quantities (#405)
- `quantity` now takes `reference` object, which aggregates `quantity_spec` and a `unit` and a `representation` type
- units, prefixes, dimensions, quantity specifications, and references are passed as NTTPs to templates and provide arithmetic operations and comparison
- expression templates consistently used in all derived types to increase the readability (#351, #166)
- derived dimensions are now factors of only base dimensions (#281)
- convertibility of derived quantities (#427)
- dimensions, quantity specifications, units, and references are now composable, significantly reducing the number of definitions and resulting types
- heavily simplified unit systems definitions (no need to define unnamed derived units, systems-specific dimensions, aliases for quantities, concepts, UDLs, ... anymore)
- improved definition of all systems
- support for ISO 80000 Part 3-6 quantities
- faster than lightspeed constants (#169)
- extensions to quantity formatting with `fmt`
- `quantity_kind` removed
- improved casting of unit with `.in(Unit)`, `.force_in(Unit)` for `quantity` and `quantity_spec`
- numerical value accessor safety improved with `.numerical_value_in(Unit)` and `.force_numerical_value_in(Unit)`
- `quantity` can no longer be constructed with a raw value (#434)
- Implicit construction of quantities from a value (#410)
- `quantity_point` can no longer be constructed with just a `quantity` and an explicit `PointOrigin` is always needed
- `ceil` and `floor` are dangerous (#432)
- quecto, ronto, ronna, quetta new SI prefixes support
- comparison against zero added (#487)
- documentation rewritten from scratch
- many smaller changes not possible to address with the previous design (#205, #210, #134)

### 0.8.0 <small>June 14, 2023</small> { id="0.8.0" }

- (!) refactor: `common_quantity`, `common_quantity_for`, `common_quantity_point`, `common_quantity_kind`, and `common_quantity_point_kind` removed
- (!) refactor: `named_derived_unit` removed as it was not used
- (!) refactor: `derived_unit` renamed to `derived_scaled_unit`
- (!) refactor: `unit` renamed to `derived_unit`
- (!) refactor: `U::is_named` removed from the unit types and replaced with `NamedUnit` concept
- (!) refactor: `PrefixFamily` support removed
- (!) refactor: `mi(naut)` renamed to `nmi`
- (!) refactor: `knot` unit helper renamed to `kn` in FPS
- (!) refactor: `knot` text symbol changed from `"knot"` to `"kn"`
- refactor: `quantity` `op+()` and `op-()` reimplemented in terms of `reference` rather then `quantity` types
- refactor(example): `glide_computer` now use dimensionless quantities with `ranged_representation` as `rep`
- feat: HEP system support added (thanks [@RalphSteinhagen](https://github.com/RalphSteinhagen))
- feat: `floor()`, `ceil()`, and `round()` support added (thanks [@hofbi](https://github.com/hofbi))
- feat: `std::format` support for compliant compilers added
- feat: conversion helpers from `mp-units` to `std::chrono` types added
- feat: math functions can now be safely used with user-defined types
- feat: conversion from `quantity_point` to `std::chrono::time_point` added
- feat: `nautical_mile_per_hour` and `knot` added to `si::international` system
- (!) fix: add `quantity_point::origin`, like `std::chrono::time_point::clock`
- fix: enable any prefixes for most of the named units (beside those that use prefixes already)
- fix: `hectare` definition fixed to be a prefixed version of `are` + other units
- fix: account for different dimensions in `quantity_point_cast`'s constraint
- fix: output stream operator now properly handles state
- fix: `fmt` algorithms were overconstrained with `forward_iterator`
- fix: CTAD for aliases fixed
- fix: `derived_ratio` calculation
- fix: `fill_t` assignment operator fixed
- fix: improve downcast mode off
- fix: `radioactivity` header compilation fixed
- fix: `si::hep::dim_momentum` duplicated definition fixed
- fix: `fps` can now coexist with `international` system
- fix: public headers fixed to be standalone
- test: standalone public headers tests added
- (!) build: CMake generator in Conan is no longer obtained from an environment variable
- (!) build: Required Conan version bumped to 1.48
- (!) build: Conan 1.48 does not set `CMAKE_BUILD_TYPE` in the `conan_toolchain.cmake` anymore
- build: AppleClang 13 support added (thanks [@fdischner](https://github.com/fdischner))
- build: most of the `conanfile.py` refactored to be Conan 2.0 ready
- build: `validate()` replaced with `configure()` to raise errors during `conan install` in Conan 1.X
- build: minimum Conan version changed to 1.40
- build: `linear-algebra` Conan repo is no needed anymore
- build: Gitpod support added
- build: clang-format-15 support added
- build: export config to local build (#322)
- build: fix export name of `mp-units-system`
- build: fmt updated to 8.0.1
- build: gsl-lite updated to 0.40.0
- build: catch2 updated to 2.13.9
- build: doxygen updated to 1.9.4
- build: linear_algebra/0.7.0 switched to wg21-linear_algebra/0.7.2
- ci: VS2022, gcc-11, clang-13, clang-14, and AppleClang 13 support added
- ci: pre-commit support added (thanks [@hofbi](https://github.com/hofbi))
- docs: Project documentation updated
- docs: `CITATION.cff` file added
- docs: `CONTRIBUTING.md` updated

### 0.7.0 <small>May 11, 2021</small> { id="0.7.0" }

- (!) refactor: `ScalableNumber` renamed to `Representation`
- (!) refactor: output stream operators moved to the `units/quantity_io.h` header file
- (!) refactor: Refactored the library file tree
- (!) refactor: `quantity::count()` renamed to `quantity::number()`
- (!) refactor: `data` system renamed to `isq::iec80000` (quantity names renamed too)
- (!) refactor: `*deduced_unit` renamed to `*derived_unit`
- (!) refactor: got rid of a `noble_derived_unit`
- refactor: quantity (kind) point updated to reflect latest changes to `quantity`
- refactor: basic concepts, `quantity` and `quantity_cast` refactored
- refactor: `abs()` definition refactored to be more explicit about the return type
- feat: quantity (point) kind support added (thanks [@johelegp](https://github.com/johelegp))
- feat: quantity references support added (thanks [@johelegp](https://github.com/johelegp))
- feat: quantity aliases support addded
- feat: interoperability with `std::chrono::duration` and other units libraries
- feat: CTAD for dimensionless quantity added
- feat: `modulation_rate` support added (thanks [@go2sh](https://github.com/go2sh))
- feat: SI prefixes for `isq::iec80000` support added (thanks [@go2sh](https://github.com/go2sh))
- feat: a possibility to disable quantity UDLs support with `UNITS_NO_LITERALS` preprocessor define
- feat: a support to define ISQ derived dimensions in terms of different number or order of components
- perf: preconditions check do not influence the runtime performance of a Release build
- perf: `quantity_cast()` generates less assembly instructions
- perf: temporary string creation removed from `quantity::op<<()`
- perf: value initialization for quantity value removed (left with a default initialization)
- perf: limited the `equivalent` trait usage
- perf: limited the C++ Standard Library headers usage
- perf: rvalue references support added for constructors and getters
- (!) fix: `exp()` has sense only for dimensionless quantities
- (!) fix: `dim_torque` now properly divides by an angle (instead of multiply) + default unit name change
- fix: quantity's operators fixed to behave like the underlying types do
- fix: `quantity_cast()` fixed to work correctly with representation types not convertible from `std::intmax_t`
- fix: ambiguous case for empty type list resolved
- fix: downcasting facility for non-default-constructible types
- fix: restore user-warnings within the library implementation
- fix: the text symbol of `foot_pound_force` and `foot_pound_force_per_second`
- fix: quantity modulo arithmetics fixed
- (!) build: Conan testing version is now hosted on [Artifactory](https://mpusz.jfrog.io/ui/packages/conan:%2F%2Fmp-units)
- (!) build: Linear Algebra is now hosted on its [Artifactory](https://twonington.jfrog.io/artifactory/api/conan/conan-oss)
- (!) build: `BUILD_DOCS` CMake option renamed to `UNITS_BUILD_DOCS`
- build: doxygen updated to 1.8.20
- build: catch2 updated to 2.13.4
- build: fmt updated to 7.1.3
- build: ms-gsl replaced with gsl-lite/0.38.0
- build: Conan generator switched to `cmake_find_package_multi`
- build: Conan CMakeToolchain support added
- build: CMake scripts cleanup
- build: ccache support added
- ci: CI switched from Travis CI to GitHub Actions

### 0.6.0 <small>September 13, 2020</small> { id="0.6.0" }

- feat: `quantity_point` support added (thanks [@johelegp](https://github.com/johelegp))
- feat: Added angle as SI base dimension (thanks [@kwikius](https://github.com/kwikius))
- feat: `si::angular_velocity` support added (thanks [@mikeford3](https://github.com/mikeford3))
- feat: FPS system added (thanks [@mikeford3](https://github.com/mikeford3))
- feat: Added support for mathematical function `exp(quantity)`
- feat: Localization support for text output added (thanks [@rbrugo](https://github.com/rbrugo))
- feat: Added STL random number distribution wrappers (thanks [@yasamoka](https://github.com/yasamoka))
- (!) refactor: Refactored and cleaned up the library file tree
- (!) refactor: `q_*` UDL renamed to `_q_*`
- (!) refactor: UDLs with "per" in name renamed from `*p*` to `*_per_*`
- (!) refactor: `ratio` changed to the NTTP kind
- (!) refactor: `exp` and `Exp` renamed to `exponent` and `Exponent`
- (!) refactor: `Scalar` concept renamed to `ScalableNumber`
- (!) refactor: Dimensionless quantities redesigned to be of a `quantity` type
- refactor: `math.h` function signatures refactored to use a `Quantity` concept (thanks [@kwikius](https://github.com/kwikius))
- refactor: `[[nodiscard]]` added to many functions
- fix: `si::day` unit symbol fixed to `d` (thanks [@komputerwiz](https://github.com/komputerwiz))
- fix: `si::mole` unit symbol fixed to `mol` (thanks [@mikeford3](https://github.com/mikeford3))
- (!) build: gcc-9 is no longer supported (at least gcc-10 is required)
- build: Visual Studio 16.7 support added
- build: linear_algebra updated to 0.7.0/stable
- build: fmt updated to 7.0.3
- build: range-v3 updated to 0.11.0
- build: catch2 updated to 2.13.0
- build: doxygen updated to 1.8.18
- build: ms-gsl 3.1.0 dependency added
- build: Removed the dependency on a git submodule with common CMake scripts

### 0.5.0 <small>May 17, 2020</small> { id="0.5.0" }

- Major refactoring and rewrite of the library
- Units are now independent from dimensions
- Dimensions now depend on units (base or coherent units are provided in a class template)
- Quantity gets a Dimension template parameter again (as unit does not provide information about
  its dimension anymore)
- Spaceship operator support added
- Added official CGS system support
- Added official data information system support
- Repository file tree cleanup
- `ratio` refactored to contain `Exp` template parameter (thanks a lot [@oschonrock](https://github.com/oschonrock)!)
- SI fundamental constants added
- `q_` prefix applied to all the UDLs (thanks [@kwikius](https://github.com/kwikius))
- `unknown_unit` renamed to `unknown_coherent_unit`
- Project documentation greatly extended and switched to Sphinx
- A few more usage examples added
- ASCII-only output support added (thanks [@yasamoka](https://github.com/yasamoka))
- Representation values formatting extended (thanks [@rbrugo](https://github.com/rbrugo))
- Output streams formatting support added
- Linear algebra from `std::experimental::math` support added
- Named SI units and their dimensions added (thanks [@rbrugo](https://github.com/rbrugo)
- libfmt updated to 6.2.0
- Added absolute functions and epsilon to math.h (thanks [@mikeford3](https://github.com/mikeford3))
- Added a lot of prefixes to named units and introduced `alias_unit` (thanks [@yasamoka](https://github.com/yasamoka))
- Linking with Conan targets only when they exists ([#98](https://github.com/mpusz/units/issues/98))
- All physical dimensions and units put into `physical` namespace
- CMake improvements
- Velocity renamed to speed

Many thanks to GitHub users [@oschonrock](https://github.com/oschonrock),
[@kwikius](https://github.com/kwikius), and [@i-ky](https://github.com/i-ky) for their support
in drafting a new library design.

### 0.4.0 <small>Nov 17, 2019</small> { id="0.4.0" }

- Support for derived dimensions in `exp` added
- Added `pow()` and `sqrt()` operations on quantities
- `units` removed from a `std::experimental` namespace
- Downcasting facility refactored so the user does not have to write the boilerplate code anymore
- From now on base dimensions should inherit from `base_dimension` class template
- Added unit symbols definitions to `base_dimension` and derived units
- Added support for `operator<<` on `quantity`
- `fmt` support added
- Derived unit factory helpers refactored
- Refactored the way prefixed units are defined

### 0.3.1 <small>Sep 18, 2019</small> { id="0.3.1" }

- cmcstl2 dependency changed to range-v3 0.9.1

### 0.3.0 <small>Sep 16, 2019</small> { id="0.3.0" }

- The design as described on CppCon 2019 talk (<https://youtu.be/0YW6yxkdhlU>)
- Applied the feedback from the Cologne evening session
  - `upcasting_traits` renamed to `downcasting_traits`
  - `Dimension` template parameter removed from quantity
- `units` moved to a `std::experimental` namespace
- Leading underscore prefix removed from UDLs
- Added a few more derived dimensions
- `meter` renamed to `metre`
- Missing `operator*` added
- Predefined dimensions moved to a dedicated directory
- `dimension_` prefix removed from names of derived dimensions
- cmcstl2 library updated to 2019.09.19
- `base_dimension` is a value provided as `const&` to the `exp` type
- integrated with Compiler Explorer
- gsl-lite dependency removed
- Fractional dimension exponents support added
- `QuantityOf` concept introduced
- `quantity_cast<U, Rep>()` support added

### 0.2.0 <small>July 18, 2019</small> { id="0.2.0" }

- The design as described on C++Now 2019 talk (<https://youtu.be/wKchCktZPHU>)
- Added C++20 features supported by gcc-9.1 (`std::remove_cvref_t`, down with typename, `std::type_identity`)
- Compile-time performance optimizations (`type_list`, `common_ratio`, `ratio`, `conditional_t`)

### 0.1.0 <small>May 18, 2019</small> { id="0.1.0" }

- Initial library release
- Begin semantic versioning
- The last version to work with gcc-8