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// Copyright 2020 The Chromium 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 BASE_CONTAINERS_CONTAINS_H_
#define BASE_CONTAINERS_CONTAINS_H_
#include <type_traits>
#include <utility>
#include "base/ranges/algorithm.h"
#include "base/ranges/ranges.h"
#include "base/template_util.h"
namespace base {
namespace internal {
// Small helper to detect whether a given type has a nested `key_type` typedef.
// Used below to catch misuses of the API for associative containers.
template <typename T, typename SFINAE = void>
struct HasKeyType : std::false_type {};
template <typename T>
struct HasKeyType<T, void_t<typename T::key_type>> : std::true_type {};
// Probe whether a `contains` member function exists and return the result of
// `container.contains(value)` if this is a valid expression. This is the
// highest priority option.
template <typename Container, typename Value>
constexpr auto ContainsImpl(const Container& container,
const Value& value,
priority_tag<2>)
-> decltype(container.contains(value)) {
return container.contains(value);
}
// Probe whether a `find` member function exists and whether its return value
// can be compared with `container.end()`. Intended for STL style maps and sets
// that lack a `contains` member function.
template <typename Container, typename Value>
constexpr auto ContainsImpl(const Container& container,
const Value& value,
priority_tag<1>)
-> decltype(container.find(value) != container.end()) {
return container.find(value) != container.end();
}
// Probe whether a `find` member function exists and whether its return value
// can be compared with `Container::npos`. Intended for STL style strings that
// lack a `contains` member function.
template <typename Container, typename Value>
constexpr auto ContainsImpl(const Container& container,
const Value& value,
priority_tag<1>)
-> decltype(container.find(value) != Container::npos) {
return container.find(value) != Container::npos;
}
// Generic fallback option, using a linear search over `container` to find
// `value`. Has the lowest priority. This will not compile for associative
// containers, as this likely is a performance bug.
template <typename Container, typename Value>
constexpr bool ContainsImpl(const Container& container,
const Value& value,
priority_tag<0>) {
static_assert(
!HasKeyType<Container>::value,
"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 ranges::find(container, value) != ranges::end(container);
}
} // namespace internal
// 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) {
return internal::ContainsImpl(container, value, internal::priority_tag<2>());
}
// Overload that allows 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 ranges::find(container, value, std::move(proj)) !=
ranges::end(container);
}
} // namespace base
#endif // BASE_CONTAINERS_CONTAINS_H_
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