concepts.hpp

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// Range v3 library
//
//  Copyright Eric Niebler 2013-present
//
//  Use, modification and distribution is subject to the
//  Boost Software License, Version 1.0. (See accompanying
//  file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)
//
// Project home: https://github.com/ericniebler/range-v3
//
#ifndef RANGES_V3_FUNCTIONAL_CONCEPTS_HPP
#define RANGES_V3_FUNCTIONAL_CONCEPTS_HPP
 
#include <concepts/concepts.hpp>
 
#include <range/v3/functional/invoke.hpp>
 
#include <range/v3/detail/prologue.hpp>
 
namespace ranges
{
 
    // clang-format off
    // WORKAROUND mysterious msvc bug
#if defined(_MSC_VER) && !defined(__clang__)
    template<typename Fun, typename... Args>
    CPP_concept invocable =
        std::is_invocable_v<Fun, Args...>;
#else
    template<typename Fun, typename... Args>
    CPP_requires(invocable_,
        requires(Fun && fn) //
        (
            invoke((Fun &&) fn, std::declval<Args>()...)
        ));
    template<typename Fun, typename... Args>
    CPP_concept invocable =
        CPP_requires_ref(ranges::invocable_, Fun, Args...);
#endif

    template<typename Fun, typename... Args>
    CPP_concept regular_invocable =
        invocable<Fun, Args...>;
        // Axiom: equality_preserving(invoke(f, args...))

    template<typename Fun, typename... Args>
    CPP_requires(predicate_,
        requires(Fun && fn) //
        (
            concepts::requires_<
                convertible_to<
                    decltype(invoke((Fun &&) fn, std::declval<Args>()...)),
                    bool>>
        ));
    template<typename Fun, typename... Args>
    CPP_concept predicate =
        regular_invocable<Fun, Args...> &&
        CPP_requires_ref(ranges::predicate_, Fun, Args...);

    template<typename R, typename T, typename U>
    CPP_concept relation =
        predicate<R, T, T> &&
        predicate<R, U, U> &&
        predicate<R, T, U> &&
        predicate<R, U, T>;

    template<typename R, typename T, typename U>
    CPP_concept strict_weak_order =
        relation<R, T, U>;
    // clang-format on
 
    namespace cpp20
    {
        using ranges::invocable;
        using ranges::predicate;
        using ranges::regular_invocable;
        using ranges::relation;
        using ranges::strict_weak_order;
    } // namespace cpp20
} // namespace ranges
 
#include <range/v3/detail/epilogue.hpp>
 
#endif