from_memory.hpp

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#pragma once
 
#include <cstddef>
#include <cstdint>
#include <new>
 
namespace from {
template <typename T>
class static_ptr {
    static_assert(sizeof(T) > 0, "T must be a complete type");
    static constexpr auto align_val = alignof(T) - 1;
 
public:
    using value_type = T;
    using pointer_type = T*;
 
    static constexpr auto size = sizeof(T);
    static constexpr auto alignment = alignof(T);
 
    pointer_type get() const noexcept {
        if (ptr && ptr->is_init) {
            std::byte* mem = ptr->memory;
            uintptr_t align_up = -reinterpret_cast<intptr_t>(mem) & align_val;
            return std::launder(reinterpret_cast<pointer_type>(mem + align_up));
        }
        return nullptr;
    }
 
    value_type& operator*() const noexcept {
        return *get();
    }
 
    pointer_type operator->() const noexcept {
        return get();
    }
 
    explicit operator bool() const noexcept {
        return static_cast<bool>(get());
    }
 
private:
    struct {
        std::byte memory[size + align_val];
        bool is_init;
    }* ptr;
};
} // namespace from