forked from mpusz/mp-units
Mateusz Pusz
37cfc53d1d
`alternative_namespaces` examples left out as I consider them a subject for removal in the nearest future.
81 lines
2.9 KiB
C++
81 lines
2.9 KiB
C++
// The MIT License (MIT)
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//
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// Copyright (c) 2018 Mateusz Pusz
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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#pragma once
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#include <units/bits/external/downcasting.h>
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#include <units/bits/basic_concepts.h>
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// IWYU pragma: begin_exports
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#include <units/ratio.h>
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#include <units/symbol_text.h>
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// IWYU pragma: end_exports
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namespace units {
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/**
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* @brief The base for all prefix families
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*
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* Every prefix family should inherit from this type to satisfy PrefixFamily concept.
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*/
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struct prefix_family {};
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/**
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* @brief No prefix possible for the unit
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*
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* This is a special prefix type tag specifying that the unit can not be scaled with any kind
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* of the prefix.
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*/
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struct no_prefix : prefix_family {};
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namespace detail {
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template<PrefixFamily PF, ratio R>
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struct prefix_base : downcast_base<prefix_base<PF, R>> {
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using prefix_family = PF;
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static constexpr ::units::ratio ratio = R;
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};
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} // namespace detail
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/**
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* @brief A prefix used to scale units
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*
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* Data from a prefix class is used in two cases:
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* - when defining a prefixed_unit its ratio is used to scale the reference unit and its
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* symbol is used to prepend to the symbol of referenced unit
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* - when printing the symbol of a scaled unit that was not predefined by the user but its
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* factor matches ratio of a prefix from the specified prefix family, its symbol will be
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* prepended to the symbol of the unit
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*
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* @tparam Child inherited class type used by the downcasting facility (CRTP Idiom)
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* @tparam PF a type of prefix family
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* @tparam Symbol a text representation of the prefix
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* @tparam R factor to be used to scale a unit
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*/
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template<typename Child, PrefixFamily PF, basic_symbol_text Symbol, ratio R>
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requires (!std::same_as<PF, no_prefix>)
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struct prefix : downcast_dispatch<Child, detail::prefix_base<PF, R>, downcast_mode::on> {
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static constexpr auto symbol = Symbol;
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};
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} // namespace units
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