FunctionConcepts.h

/*
  ==============================================================================
    DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 
    Copyright 2022- by sonible GmbH.
 
    This file is part of VCTR - Versatile Container Templates Reconceptualized.
 
    VCTR is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License version 3
    only, as published by the Free Software Foundation.
 
    VCTR is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License version 3 for more details.
 
    You should have received a copy of the GNU Lesser General Public License
    version 3 along with VCTR.  If not, see <https://www.gnu.org/licenses/>.
  ==============================================================================
*/
 
namespace vctr::detail
{
 
template <class, class>
struct FunctionWithSignature : std::false_type
{
};
 
template <class Fn, class Ret, class... Args>
struct FunctionWithSignature<Fn, Ret (Args...)>
{
    static constexpr bool value = requires (Fn&& t, Ret (*fp) (Args...)) { fp = &t; };
};
 
template <class, class>
struct FunctionWithSignatureOrImplicitlyConvertible : std::false_type
{
};
 
template <class Fn, class Ret, class... Args>
struct FunctionWithSignatureOrImplicitlyConvertible<Fn, Ret (Args...)>
{
    static constexpr bool value = requires (Fn&& t, Args&&... args) { { t (args...) } -> std::convertible_to<Ret>; };
};
 
} // namespace vctr::detail
 
namespace vctr::is
{
 
template <class Fn, class Signature>
concept functionWithSignature = detail::FunctionWithSignature<Fn, Signature>::value;
 
template <class Fn, class Signature>
concept functionWithSignatureOrImplicitlyConvertible = detail::FunctionWithSignatureOrImplicitlyConvertible<Fn, Signature>::value;
 
} // namespace vctr::is