formatter.h

Go to the documentation of this file.

#pragma once
// SPDX-FileCopyrightText: 2025 Nessan Fitzmaurice <nzznfitz+gh@icloud.com>
// SPDX-License-Identifier: MIT

 
#include <concepts>
#include <format>
#include <cassert>
 
namespace utilities {

template<typename T>
concept has_to_string = requires(const T& x) {
    { x.to_string() } -> std::convertible_to<std::string>;
};
 
} // namespace utilities

template<utilities::has_to_string T>
struct std::formatter<T> {
    template<class FormatContext>
    auto format(const T& rhs, FormatContext& ctx) const
    {
        return std::format_to(ctx.out(), "{}", rhs.to_string());
    }
 
    constexpr auto parse(const std::format_parse_context& ctx)
    {
        // Throw an error for anything that is not default formatted.
        // The `to_string()` method might handle various formatting options, but we cannot know that here.
        auto it = ctx.begin();
        assert(it == ctx.end() || *it == '}');
        return it;
    }
};