meta.h

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#pragma once
 
#include "../stream/serialize_traits.h"
 
#include <type_traits>
 
namespace bitstream::utility
{
    // Check if type has a serializable trait
    template<typename Void, typename T, typename Stream, typename... Args>
    struct has_serialize : std::false_type {};
 
    template<typename T, typename Stream, typename... Args>
    struct has_serialize<std::void_t<decltype(serialize_traits<T>::serialize(std::declval<Stream&>(), std::declval<Args>()...))>, T, Stream, Args...> : std::true_type {};
 
    template<typename T, typename Stream, typename... Args>
    using has_serialize_t = std::void_t<decltype(serialize_traits<T>::serialize(std::declval<Stream&>(), std::declval<Args>()...))>;
 
    template<typename T, typename Stream, typename... Args>
    constexpr bool has_serialize_v = has_serialize<void, T, Stream, Args...>::value;
 
 
    // Check if stream is writing or reading
    template<typename T, typename R = bool>
    using is_writing_t = std::enable_if_t<T::writing, R>;
 
    template<typename T, typename R = bool>
    using is_reading_t = std::enable_if_t<T::reading, R>;
 
 
    // Check if type is noexcept, if it exists
    template<typename Void, typename T, typename Stream, typename... Args>
    struct is_serialize_noexcept : std::false_type {};
 
    template<typename T, typename Stream, typename... Args>
    struct is_serialize_noexcept<std::enable_if_t<has_serialize_v<T, Stream, Args...>>, T, Stream, Args...> :
        std::bool_constant<noexcept(serialize_traits<T>::serialize(std::declval<Stream&>(), std::declval<Args>()...))> {};
 
    template<typename T, typename Stream, typename... Args>
    constexpr bool is_serialize_noexcept_v = is_serialize_noexcept<void, T, Stream, Args...>::value;
 
 
    // Get the underlying type without &, &&, * or const
    template<typename T>
    using base_t = typename std::remove_const_t<std::remove_pointer_t<std::decay_t<T>>>;
 
 
    // Meta functions for guessing the trait type from the first argument
    template<typename Void, typename Trait, typename Stream, typename... Args>
    struct deduce_trait
    {
        using type = Trait;
    };
 
    // Non-const value
    template<typename Trait, typename Stream, typename... Args>
    struct deduce_trait<std::enable_if_t<
        !std::is_pointer_v<std::decay_t<Trait>> &&
        has_serialize_v<base_t<Trait>, Stream, Trait, Args...>>,
        Trait, Stream, Args...>
    {
        using type = base_t<Trait>;
    };
 
    // Const value
    template<typename Trait, typename Stream, typename... Args>
    struct deduce_trait<std::enable_if_t<
        !std::is_pointer_v<std::decay_t<Trait>> &&
        has_serialize_v<std::add_const_t<base_t<Trait>>, Stream, Trait, Args...>>,
        Trait, Stream, Args...>
    {
        using type = std::add_const_t<base_t<Trait>>;
    };
 
    // Non-const pointer
    template<typename Trait, typename Stream, typename... Args>
    struct deduce_trait<std::enable_if_t<
        std::is_pointer_v<std::decay_t<Trait>> &&
        has_serialize_v<std::add_pointer_t<base_t<Trait>>, Stream, Trait, Args...>>,
        Trait, Stream, Args...>
    {
        using type = std::add_pointer_t<base_t<Trait>>;
    };
 
    // Const pointer
    template<typename Trait, typename Stream, typename... Args>
    struct deduce_trait<std::enable_if_t<
        std::is_pointer_v<std::decay_t<Trait>> &&
        has_serialize_v<std::add_pointer_t<std::add_const_t<base_t<Trait>>>, Stream, Trait, Args...>>,
        Trait, Stream, Args...>
    {
        using type = std::add_pointer_t<std::add_const_t<base_t<Trait>>>;
    };
 
    template<typename Trait, typename Stream, typename... Args>
    using deduce_trait_t = typename deduce_trait<void, Trait, Stream, Args...>::type;
 
 
    // Shorthands for deduced type_traits
    template<typename Trait, typename Stream, typename... Args>
    using has_deduce_serialize_t = has_serialize_t<deduce_trait_t<Trait, Stream, Args...>, Stream, Trait, Args...>;
 
    template<typename Trait, typename Stream, typename... Args>
    constexpr bool is_deduce_serialize_noexcept_v = is_serialize_noexcept_v<deduce_trait_t<Trait, Stream, Args...>, Stream, Trait, Args...>;
}