98 lines
3.9 KiB
C++
98 lines
3.9 KiB
C++
// 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_
|
|
|
|
#include <type_traits>
|
|
#include <utility>
|
|
|
|
#include "base/ranges/algorithm.h"
|
|
#include "base/ranges/ranges.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, std::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_
|