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// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_CONTAINERS_CONTAINS_H_
#define BASE_CONTAINERS_CONTAINS_H_
// Provides `Contains()`, a general purpose utility to check whether a container
// contains a value. This will probe whether a `contains` or `find` member
// function on `container` exists, and fall back to a generic linear search over
// `container`.
#include <algorithm>
#include <concepts>
#include <ranges>
#include <utility>
namespace base {
// A general purpose utility to check whether `container` contains `value`. This
// will probe whether a `contains` or `find` member function on `container`
// exists, and fall back to a generic linear search over `container`.
template <typename Container, typename Value>
constexpr bool Contains(const Container& container, const Value& value) {
if constexpr (requires {
{ container.contains(value) } -> std::same_as<bool>;
}) {
return container.contains(value);
} else if constexpr (requires { container.find(value) != Container::npos; }) {
return container.find(value) != Container::npos;
} else if constexpr (requires { container.find(value) != container.end(); }) {
return container.find(value) != container.end();
} else {
static_assert(
!requires { typename Container::key_type; },
"Error: About to perform linear search on an associative container. "
"Either use a more generic comparator (e.g. std::less<>) or, if a "
"linear search is desired, provide an explicit projection parameter.");
return std::ranges::find(container, value) != std::ranges::end(container);
}
}
// Overload that allows callers to provide an additional projection invocable.
// This projection will be applied to every element in `container` before
// comparing it with `value`. This will always perform a linear search.
template <typename Container, typename Value, typename Proj>
constexpr bool Contains(const Container& container,
const Value& value,
Proj proj) {
return std::ranges::find(container, value, std::move(proj)) !=
std::ranges::end(container);
}
} // namespace base
#endif // BASE_CONTAINERS_CONTAINS_H_
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