636b133cbc
A type trait (is_variant_element) and a concept (VariantElement) that tell if a type T is a member of a variant or not. It can be used even if the variant's elements are not yet defined (just forward-declared).
50 lines
1.5 KiB
C++
50 lines
1.5 KiB
C++
/*
|
|
* Copyright (C) 2021-present ScyllaDB
|
|
*/
|
|
|
|
/*
|
|
* This file is part of Scylla.
|
|
*
|
|
* Scylla is free software: you can redistribute it and/or modify
|
|
* it under the terms of the GNU Affero General Public License as published by
|
|
* the Free Software Foundation, either version 3 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* Scylla is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#pragma once
|
|
|
|
#include <variant>
|
|
#include <type_traits>
|
|
|
|
namespace utils {
|
|
|
|
// Given type T and an std::variant Variant, return std::true_type if T is a variant element
|
|
// This is also the recursion base case (empty variant), so return false.
|
|
template <typename T, typename Variant>
|
|
struct is_variant_element : std::false_type {
|
|
};
|
|
|
|
// Match - return true
|
|
template <typename T, typename... Elements>
|
|
struct is_variant_element<T, std::variant<T, Elements...>> : std::true_type {
|
|
};
|
|
|
|
// No match - recurse
|
|
template <typename T, typename U, typename... Elements>
|
|
struct is_variant_element<T, std::variant<U, Elements...>> : is_variant_element<T, std::variant<Elements...>> {
|
|
};
|
|
|
|
// Givent type T and std::variant, true if T is one of the variant elements.
|
|
template <typename T, typename Variant>
|
|
concept VariantElement = is_variant_element<T, Variant>::value;
|
|
|
|
}
|