delayed_format.hpp

// Copyright Take Vos 2021.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#include <fmt/format.h>
#include <tuple>
#include "forward_value.hpp"
#include "fixed_string.hpp"
 
#pragma once
 
namespace tt {
 
template<basic_fixed_string Fmt, typename... Values>
class delayed_format {
public:
    static_assert(std::is_same_v<decltype(Fmt)::value_type, char>, "Fmt must be a basic_fixed_string<char>");
 
    delayed_format(delayed_format &&) noexcept = default;
    delayed_format(delayed_format const &) noexcept = default;
    delayed_format &operator=(delayed_format &&) noexcept = default;
    delayed_format &operator=(delayed_format const &) noexcept = default;
 
    template<typename... Args>
    delayed_format(Args &&...args) noexcept : _values(forward_value<Args>{}(args)...)
    {
    }
 
    [[nodiscard]] std::string operator()() const noexcept
    {
        auto tmp = std::tuple_cat(std::tuple{static_cast<char const *>(Fmt)}, _values);
        return std::apply(fmt::format<char const *,Values const &...>, std::move(tmp));
    }
 
    [[nodiscard]] std::string operator()(std::locale const &loc) const noexcept
    {
        tt_not_implemented();
    }
 
private:
    std::tuple<Values...> _values;
};
 
template<fixed_string Fmt, typename... Args>
delayed_format(Args &&...) -> delayed_format<Fmt, forward_value_t<Args>...>;
 
} // namespace tt