meta.h

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#pragma once
 
#include <type_traits>
 
namespace ktl::detail
{
    // has value_type
    template<typename Alloc, typename = void>
    struct has_no_value_type : std::true_type {};
 
    template<typename Alloc>
    struct has_no_value_type<Alloc, std::void_t<typename Alloc::value_type>> : std::false_type {};
 
    template<typename Alloc>
    constexpr bool has_no_value_type_v = has_no_value_type<Alloc, void>::value;
 
    // get size_type
    template<typename Alloc, typename = void>
    struct get_size_type
    {
        using type = size_t;
    };
 
    template<typename Alloc>
    struct get_size_type<Alloc, std::void_t<typename Alloc::size_type>>
    {
        using type = typename Alloc::size_type;
    };
 
    template<typename Alloc>
    using get_size_type_t = typename get_size_type<Alloc, void>::type;
 
    // has construct(T*, Args&&...)
    template<typename Void, typename... Types>
    struct has_construct : std::false_type {};
 
    template<typename Alloc, typename... Args>
    struct has_construct<std::void_t<decltype(std::declval<Alloc&>().construct(std::declval<Args>()...))>, Alloc, Args...> : std::true_type {};
 
    template<typename Alloc, typename... Args>
    constexpr bool has_construct_v = has_construct<void, Alloc, Args...>::value;
 
    // has destroy(T*)
    template<typename Alloc, typename Ptr, typename = void>
    struct has_destroy : std::false_type {};
 
    template<typename Alloc, typename Ptr>
    struct has_destroy<Alloc, Ptr, std::void_t<decltype(std::declval<Alloc&>().destroy(std::declval<Ptr>()))>> : std::true_type {};
 
    template<typename Alloc, typename Ptr>
    constexpr bool has_destroy_v = has_destroy<Alloc, Ptr, void>::value;
 
    // has max_size()
    template<typename Alloc, typename = void>
    struct has_max_size : std::false_type {};
 
    template<typename Alloc>
    struct has_max_size<Alloc, std::void_t<decltype(std::declval<Alloc&>().max_size())>> : std::true_type {};
 
    template<typename Alloc>
    constexpr bool has_max_size_v = has_max_size<Alloc, void>::value;
 
    // has owns(void*)
    template<typename Alloc, typename = void>
    struct has_owns : std::false_type {};
 
    template<typename Alloc>
    struct has_owns<Alloc, std::void_t<decltype(std::declval<Alloc&>().owns(std::declval<void*>()))>> : std::true_type {};
 
    template<typename Alloc>
    constexpr bool has_owns_v = has_owns<Alloc, void>::value;
 
 
 
    // has allocate(size_t) noexcept
    template<typename Alloc>
    constexpr bool has_nothrow_allocate_v = noexcept(std::declval<Alloc&>().allocate(std::declval<size_t>()));
 
    // has deallocate(void*, size_t) noexcept
    template<typename Alloc>
    constexpr bool has_nothrow_deallocate_v = noexcept(std::declval<Alloc&>().deallocate(std::declval<void*>(), std::declval<size_t>()));
 
    // has T& == T& noexcept
    template<typename T>
    constexpr bool has_nothrow_equal_v = noexcept(std::declval<T&>() == std::declval<T&>());
 
    // has T& == T& noexcept
    template<typename T>
    constexpr bool has_nothrow_not_equal_v = noexcept(std::declval<T&>() == std::declval<T&>());
 
    // has construct(T*, Args&&...) noexcept
    template<typename Void, typename... Types>
    struct has_nothrow_construct : std::false_type {};
 
    template<typename Alloc, typename... Args>
    struct has_nothrow_construct<std::enable_if_t<has_construct_v<Alloc, Args...>>, Alloc, Args...>
        : std::bool_constant<noexcept(std::declval<Alloc&>().construct(std::declval<Args>()...))> {};
 
    template<typename Alloc, typename... Args>
    constexpr bool has_nothrow_construct_v = has_nothrow_construct<void, Alloc, Args...>::value;
 
    // has destroy(T*) noexcept
    template<typename Alloc, typename Ptr, typename = void>
    struct has_nothrow_destroy : std::false_type {};
 
    template<typename Alloc, typename Ptr>
    struct has_nothrow_destroy<Alloc, Ptr, std::enable_if_t<has_destroy_v<Alloc, Ptr>>>
        : std::bool_constant<noexcept(std::declval<Alloc&>().destroy(std::declval<Ptr>()))> {};
 
    template<typename Alloc, typename Ptr>
    constexpr bool has_nothrow_destroy_v = has_nothrow_destroy<Alloc, Ptr, void>::value;
 
    // has max_size() noexcept
    template<typename Alloc, typename = void>
    struct has_nothrow_max_size : std::false_type {};
 
    template<typename Alloc>
    struct has_nothrow_max_size<Alloc, std::enable_if_t<has_max_size_v<Alloc>>>
        : std::bool_constant<noexcept(std::declval<Alloc&>().max_size())> {};
 
    template<typename Alloc>
    constexpr bool has_nothrow_max_size_v = has_nothrow_max_size<Alloc, void>::value;
 
    // has owns(void*) noexcept
    template<typename Alloc, typename = void>
    struct has_nothrow_owns : std::false_type {};
 
    template<typename Alloc>
    struct has_nothrow_owns<Alloc, std::enable_if_t<has_owns_v<Alloc>>>
        : std::bool_constant<noexcept(std::declval<Alloc&>().owns(std::declval<void*>()))> {};
 
    template<typename Alloc>
    constexpr bool has_nothrow_owns_v = has_nothrow_owns<Alloc, void>::value;
}