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// Copyright 2019 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef LIBBRILLO_BRILLO_TYPE_LIST_H_
#define LIBBRILLO_BRILLO_TYPE_LIST_H_
#include <type_traits>
namespace brillo {
template <typename... Ts>
struct TypeList {};
namespace type_list {
template <typename... Ts>
struct is_one_of {
static constexpr bool value = false;
};
template <typename T, typename Head, typename... Tail>
struct is_one_of<T, TypeList<Head, Tail...>> {
static constexpr bool value =
std::is_same<T, Head>::value || is_one_of<T, TypeList<Tail...>>::value;
};
} // namespace type_list
// Enables a template if the type T is in the typelist Types. Since std::same is
// used to determine equivalence of types, cv-qualifiers (const and volatile)
// *are* important. Note that typedefs and type aliases do not define new types.
//
// Example:
// using ValidTypes = TypeList<int32_t, float>;
//
// template <typename T, typename = EnableIfIsOneOf<T, ValidTypes>>
// void f(){}
//
// using integer = int32_t;
// ...
// f<int32_t>(); // Fine.
// f<float>(); // Fine.
// f<integer>(); // Fine.
// f<const int32_t>(); // Error; no matching function for call to 'f'.
// f<uint32_t>(); // Error; no matching function for call to 'f'.
template <typename T, typename Types>
using EnableIfIsOneOf =
std::enable_if_t<type_list::is_one_of<T, Types>::value>;
} // namespace brillo
#endif // LIBBRILLO_BRILLO_TYPE_LIST_H_
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