libcruft-util/cruft/util/fixed_string.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2019, Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include <string_view>


///////////////////////////////////////////////////////////////////////////////
namespace cruft {
    /// A simple string-like class that allows constexpr representation of
    /// strings.
    ///
    /// This allows strings to be represented as instances of fixed_string in
    /// template parameters (rather than using vendor specific array
    /// extensions).
    template <std::size_t N>
    struct fixed_string {
        using value_type = char;

        char value[N + 1] {};

        static std::size_t size (void) { return N; }

        constexpr
        fixed_string (char const _value[N+1]) noexcept
        {
            for (std::size_t i = 0; i <= N; ++i)
                value[i] = _value[i];
        }

        constexpr operator char const* () const { return value; }
        constexpr operator std::string_view () const { return value; }

        constexpr char const*
        c_str (void) const noexcept
        { return value; }

        auto begin (void) const& noexcept { return std::begin (value); }
        auto end   (void) const& noexcept { return std::end   (value); }


        constexpr bool
        operator== (fixed_string<N> const&) const noexcept = default;

        template <std::size_t M>
        requires (M != N)
        constexpr bool
        operator== (fixed_string<M> const&) const noexcept
        { return false; }
    };

    template <std::size_t N>
    fixed_string (char const (&)[N]) -> fixed_string<N - 1>;
}