eonix/gblibstdc++/include/memory

#ifndef __GBLIBCPP_MEMORY__
#define __GBLIBCPP_MEMORY__

#include <cstddef>
#include <type_traits>
#include <utility>

namespace std {

template <typename T>
constexpr T* addressof(T& arg) noexcept
{
    return __builtin_addressof(arg);
}

// template <typename T>
// constexpr enable_if_t<is_function_v<remove_reference_t<T>>, T*>
// addressof(T& arg) noexcept
// {
//     return &arg;
// }

// template <typename T>
// constexpr enable_if_t<!is_function_v<remove_reference_t<T>>, T*>
// addressof(T& arg) noexcept
// {
//     return reinterpret_cast<T*>(
//         &const_cast<char&>(
//             reinterpret_cast<const volatile char&>(arg)
//         )
//     );
// }

template <typename T>
const T* addressof(const T&&) = delete;

template <typename T>
struct allocator {
    using value_type = T;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;

    constexpr allocator() noexcept = default;
    constexpr allocator(const allocator& other) noexcept = default;

    template <typename U>
    constexpr allocator(const allocator<U>&) noexcept {}

    constexpr ~allocator() = default;

    // throws std::bad_alloc
    [[nodiscard]] constexpr T* allocate(std::size_t n)
    { return static_cast<T*>(::operator new(n * sizeof(T))); }

    // TODO: check allocated size
    constexpr void deallocate(T* ptr, std::size_t)
    { ::operator delete(ptr); }
};

template <typename T1, typename T2>
constexpr bool operator==(const allocator<T1>&, const allocator<T2>&) noexcept
{ return true; }

template <typename T, typename... Args>
constexpr std::enable_if_t<std::is_same_v<T*,
    decltype(::new(std::declval<void*>()) T(std::declval<Args>()...))> , T*>
construct_at(T* p, Args&&... args)
{
    return ::new (static_cast<void*>(p)) T(std::forward<Args>(args)...);
}

template <typename T>
constexpr void destroy_at(T* p)
{
    // TODO: destroy array
    p->~T();
}

namespace __helpers {

template <typename Allocator, typename T>
struct rebind;

template <template <typename, typename...> typename Allocator,
    typename NewType, typename OldType, typename... Args>
struct rebind<Allocator<OldType, Args...>, NewType> {
    using type = Allocator<NewType, Args...>;
};

} // namespace __helpers

template <typename Allocator>
struct allocator_traits {
    using allocator_type = Allocator;
    using value_type = typename Allocator::value_type;
    using pointer = value_type*;
    using size_type = std::size_t;

    template <typename T>
    using rebind_alloc = typename __helpers::rebind<Allocator, T>::type;

    [[nodiscard]] static constexpr pointer allocate(Allocator& alloc, size_type n)
    { return alloc.allocate(n); }
    static constexpr void deallocate(Allocator& alloc, pointer p, size_type n)
    { return alloc.deallocate(p, n); }
    template <typename T, typename... Args>
    static constexpr void construct(Allocator&, T* p, Args&&... args)
    { std::construct_at(p, std::forward<Args>(args)...); }
    template <typename T>
    static constexpr void destroy(Allocator&, T* p)
    { std::destroy_at(p); }
};

} // namespace std

#endif