/*
 * 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 2017-2019 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include <cstdint>

namespace cruft {
    namespace detail { int typeidx_next (void); }

    /// Return a globally unique runtime ID for a given type.
    ///
    /// This is intended to be used as a lightweight type check for variants
    /// and such without requiring RTTI.
    ///
    /// The identifier is constructed at runtime and is not guaranteed to be
    /// stable across executions (particularly in the case of threads and
    /// other non-determinism). However it _is_ threadsafe to call this.
    ///
    /// The value 0 will never be returned from this function and can be used
    /// to indicate an 'unknown' state.
    ///
    /// The range of identifiers is _probably_ contiguous. This should not
    /// be relied upon for correctness, but may be used for performance
    /// concerns.
    template <typename T>
    int
    typeidx (void)
    {
        static auto id = detail::typeidx_next ();
        return id;
    }
}