string_constant.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2024 Tobias Hienzsch
 
#ifndef TETL_STRING_STRING_CONSTANT_HPP
#define TETL_STRING_STRING_CONSTANT_HPP
 
#include <etl/_array/array.hpp>
#include <etl/_cstddef/size_t.hpp>
#include <etl/_iterator/size.hpp>
#include <etl/_string_view/basic_string_view.hpp>
#include <etl/_utility/index_sequence.hpp>
 
namespace etl {
 
template <typename CharT, CharT... Chars>
struct string_constant {
    using value_type       = CharT;
    using string_view_type = etl::basic_string_view<CharT>;
 
    static constexpr auto storage = etl::array<CharT, sizeof...(Chars)>{Chars...};
 
    static constexpr auto size() noexcept
    {
        return storage.size();
    }
 
    static constexpr auto begin() noexcept
    {
        return storage.cbegin();
    }
 
    static constexpr auto end() noexcept
    {
        return storage.cend();
    }
 
    [[nodiscard]] constexpr operator string_view_type() const noexcept
    {
        return {storage.data(), storage.size()};
    }
};
 
template <typename CharT, CharT... Chars>
[[nodiscard]] constexpr auto
operator==(string_constant<CharT, Chars...> /*lhs*/, string_constant<CharT, Chars...> /*rhs*/) noexcept -> bool
{
    return true;
}
 
template <typename CharT, CharT... CharsL, CharT... CharsR>
[[nodiscard]] constexpr auto
operator==(string_constant<CharT, CharsL...> /*lhs*/, string_constant<CharT, CharsR...> /*rhs*/) noexcept -> bool
{
    return false;
}
 
namespace detail {
 
template <auto CharArray>
    requires(etl::size(CharArray) > 0)
consteval auto to_string_constant()
{
    return []<etl::size_t... Is>(etl::index_sequence<Is...> /*i*/) {
        return etl::string_constant<char, etl::get<Is>(CharArray)...>{};
    }(etl::make_index_sequence<etl::size(CharArray) - 1>{});
}
 
} // namespace detail
 
} // namespace etl
 
#define TETL_STRING_C(str) etl::detail::to_string_constant<etl::to_array(str)>()
 
#endif // TETL_STRING_STRING_CONSTANT_HPP