标准库头文件 <concepts> (C++20)

 

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标准库头文件

语言支持
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <stdfloat> (C++23) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11) <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
概念
<concepts> (C++20)
诊断
<stdexcept> <stacktrace> (C++23)	<cassert>	<cerrno>	<system_error> (C++11)
内存管理
<memory>	<memory_resource> (C++17)	<scoped_allocator> (C++11)
元编程
<type_traits> (C++11)	<ratio> (C++11)
通用实用程序
<utility> <tuple> (C++11) <optional> (C++17) <variant> (C++17)	<any> (C++17) <debugging> (C++26) <expected> (C++23) <bitset>	<functional> <typeindex> (C++11) <execution> (C++17)	<charconv> (C++17) <format> (C++20) <bit> (C++20)
字符串
<string_view> (C++17) <string>	<cctype> <cwctype>	<cstring> <cwchar>	<cuchar> (C++11)
容器
<array> (C++11) <deque> <forward_list> (C++11) <list>	<vector> <map> <set> <unordered_map> (C++11)	<unordered_set> (C++11) <queue> <stack> <flat_map> (C++23)	<flat_set> (C++23) <span> (C++20) <mdspan> (C++23) <inplace_vector> (C++26)
迭代器
<iterator>
范围
<ranges> (C++20)	<generator> (C++23)
算法
<algorithm>	<numeric>
数值
<cfenv> (C++11) <complex>	<random> (C++11) <valarray>	<cmath> <linalg> (C++26)	<numbers> (C++20)
时间
<chrono> (C++11)	<ctime>
本地化
<locale>	<clocale>	<codecvt> (C++11/17/26*)	<text_encoding> (C++26)
输入/输出
<iosfwd> <iostream> <ios> <streambuf>	<istream> <ostream> <iomanip> <print> (C++23)	<sstream> <spanstream> (C++23) <fstream> <syncstream> (C++20)	<filesystem> (C++17) <cstdio> <cinttypes> (C++11) <strstream> (C++98/26*)
正则表达式
<regex> (C++11)
并发支持
<stop_token> (C++20) <thread> (C++11) <atomic> (C++11) <rcu> (C++26)	<stdatomic.h> (C++23) <mutex> (C++11) <shared_mutex> (C++14)	<condition_variable> (C++11)   <semaphore> (C++20) <latch> (C++20)	<barrier> (C++20) <future> (C++11) <hazard_pointer> (C++26)
C 兼容性
<cstdbool> (C++11/17/20*)   <ccomplex> (C++11/17/20*)	<ctgmath> (C++11/17/20*)	<cstdalign> (C++11/17/20*)	<ciso646> (直到 C++20)

 

此头文件是 概念 库的一部分。

概念
核心语言概念
same_as (C++20)	指定一个类型与另一个类型相同 (概念)
derived_from (C++20)	指定一个类型派生自另一个类型 (概念)
convertible_to (C++20)	指定一个类型隐式可转换为另一个类型 (概念)
common_reference_with (C++20)	指定两个类型共享一个公共引用类型 (概念)
common_with (C++20)	指定两个类型共享一个公共类型 (概念)
integral (C++20)	指定一个类型是整数类型 (概念)
signed_integral (C++20)	指定一个类型是有符号的整数类型 (概念)
unsigned_integral (C++20)	指定一个类型是无符号的整数类型 (概念)
floating_point (C++20)	指定一个类型是浮点类型 (概念)
assignable_from (C++20)	指定一个类型可以从另一个类型赋值 (概念)
swappableswappable_with (C++20)	指定一个类型可以交换或两个类型可以相互交换 (概念)
destructible (C++20)	指定该类型对象可以被销毁 (概念)
constructible_from (C++20)	指定该类型变量可以从一组参数类型构造或绑定 (概念)
default_initializable (C++20)	指定该类型对象可以默认构造 (概念)
move_constructible (C++20)	指定该类型对象可以移动构造 (概念)
copy_constructible (C++20)	指定该类型对象可以复制构造和移动构造 (概念)
比较概念
equality_comparableequality_comparable_with (C++20)	指定运算符 == 是一个等价关系 (概念)
totally_orderedtotally_ordered_with (C++20)	指定该类型上的比较运算符产生一个全序 (概念)
对象概念
movable (C++20)	指定该类型对象可以移动和交换 (概念)
copyable (C++20)	指定该类型对象可以复制、移动和交换 (概念)
semiregular (C++20)	指定该类型对象可以复制、移动、交换和默认构造 (概念)
regular (C++20)	指定一个类型是正则的，也就是说，它既是 semiregular 又是 equality_comparable (概念)
可调用概念
invocableregular_invocable (C++20)	指定一个可调用类型可以用给定的一组参数类型调用 (概念)
predicate (C++20)	指定一个可调用类型是一个布尔谓词 (概念)
relation (C++20)	指定一个可调用类型是一个二元关系 (概念)
equivalence_relation (C++20)	指定一个 relation 强加了一个等价关系 (概念)
strict_weak_order (C++20)	指定一个 relation 强加了一个严格弱序 (概念)
自定义点对象
ranges::swap (C++20)	交换两个对象的值 (自定义点对象)

提要

// all freestanding
namespace std {
  // language-related concepts
  // concept same_as
  template<class T, class U>
  concept same_as = /* see description */;
 
  // concept derived_from
  template<class Derived, class Base>
  concept derived_from = /* see description */;
 
  // concept convertible_to
  template<class From, class To>
  concept convertible_to = /* see description */;
 
  // concept common_reference_with
  template<class T, class U>
  concept common_reference_with = /* see description */;
 
  // concept common_with
  template<class T, class U>
  concept common_with = /* see description */;
 
  // arithmetic concepts
  template<class T>
  concept integral = /* see description */;
  template<class T>
  concept signed_integral = /* see description */;
  template<class T>
  concept unsigned_integral = /* see description */;
  template<class T>
  concept floating_point = /* see description */;
 
  // concept assignable_from
  template<class LHS, class RHS>
  concept assignable_from = /* see description */;
 
  // concept swappable
  namespace ranges {
    inline namespace /* unspecified */ {
      inline constexpr /* unspecified */ swap = /* unspecified */;
    }
  }
  template<class T>
  concept swappable = /* see description */;
  template<class T, class U>
  concept swappable_with = /* see description */;
 
  // concept destructible
  template<class T>
  concept destructible = /* see description */;
 
  // concept constructible_from
  template<class T, class... Args>
  concept constructible_from = /* see description */;
 
  // concept default_initializable
  template<class T>
  concept default_initializable = /* see description */;
 
  // concept move_constructible
  template<class T>
  concept move_constructible = /* see description */;
 
  // concept copy_constructible
  template<class T>
  concept copy_constructible = /* see description */;
 
  // comparison concepts
  // concept equality_comparable
  template<class T>
  concept equality_comparable = /* see description */;
  template<class T, class U>
  concept equality_comparable_with = /* see description */;
 
  // concept totally_ordered
  template<class T>
  concept totally_ordered = /* see description */;
  template<class T, class U>
  concept totally_ordered_with = /* see description */;
 
  // object concepts
  template<class T>
  concept movable = /* see description */;
  template<class T>
  concept copyable = /* see description */;
  template<class T>
  concept semiregular = /* see description */;
  template<class T>
  concept regular = /* see description */;
 
  // callable concepts
  // concept invocable
  template<class F, class... Args>
  concept invocable = /* see description */;
 
  // concept regular_invocable
  template<class F, class... Args>
  concept regular_invocable = /* see description */;
 
  // concept predicate
  template<class F, class... Args>
  concept predicate = /* see description */;
 
  // concept relation
  template<class R, class T, class U>
  concept relation = /* see description */;
 
  // concept equivalence_relation
  template<class R, class T, class U>
  concept equivalence_relation = /* see description */;
 
  // concept strict_weak_order
  template<class R, class T, class U>
  concept strict_weak_order = /* see description */;
}

辅助概念 boolean-testable

template<class T>
concept /*boolean-testable-impl*/ = convertible_to<T, bool>; // exposition only;
 
template<class T>
concept boolean-testable = // exposition only
  /*boolean-testable-impl*/<T> && requires(T&& t) {
    {
      !std::forward<T>(t)
    } -> /*boolean-testable-impl*/;
  };

概念 same_as

template<class T, class U>
concept /*same-as-impl*/ = is_same_v<T, U>; // exposition only
 
template<class T, class U>
concept same_as = /*same-as-impl*/<T, U> && /*same-as-impl*/<U, T>;

概念 derived_from

template<class Derived, class Base>
concept derived_from = is_base_of_v<Base, Derived> &&
                       is_convertible_v<const volatile Derived*, const volatile Base*>;

概念 convertible_to

template<class From, class To>
concept convertible_to =
  is_convertible_v<From, To> && requires { static_cast<To>(declval<From>()); };

概念 common_reference_with

template<class T, class U>
concept common_reference_with =
  same_as<common_reference_t<T, U>, common_reference_t<U, T>> &&
  convertible_to<T, common_reference_t<T, U>> &&
  convertible_to<U, common_reference_t<T, U>>;

概念 common_with

template<class T, class U>
concept common_with =
  same_as<common_type_t<T, U>, common_type_t<U, T>> &&
  requires {
    static_cast<common_type_t<T, U>>(declval<T>());
    static_cast<common_type_t<T, U>>(declval<U>());
  } &&
  common_reference_with<add_lvalue_reference_t<const T>,
                        add_lvalue_reference_t<const U>> &&
  common_reference_with<
    add_lvalue_reference_t<common_type_t<T, U>>,
    common_reference_t<add_lvalue_reference_t<const T>, add_lvalue_reference_t<const U>>>;

概念 integral

template<class T>
concept integral = is_integral_v<T>;

概念 signed_integral

template<class T>
concept signed_integral = integral<T> && is_signed_v<T>;

概念 unsigned_integral

template<class T>
concept unsigned_integral = integral<T> && !signed_integral<T>;

概念 floating_point

template<class T>
concept floating_point = is_floating_point_v<T>;

概念 assignable_from

template<class LHS, class RHS>
concept assignable_from =
  is_lvalue_reference_v<LHS> &&
  common_reference_with<const remove_reference_t<LHS>&, const remove_reference_t<RHS>&> &&
  requires(LHS lhs, RHS&& rhs) {
    {
      lhs = std::forward<RHS>(rhs)
    } -> same_as<LHS>;
  };

概念 swappable

template<class T>
concept swappable = requires(T& a, T& b) { ranges::swap(a, b); };

概念 swappable_with

template<class T, class U>
concept swappable_with = common_reference_with<T, U> && requires(T&& t, U&& u) {
  ranges::swap(std::forward<T>(t), std::forward<T>(t));
  ranges::swap(std::forward<U>(u), std::forward<U>(u));
  ranges::swap(std::forward<T>(t), std::forward<U>(u));
  ranges::swap(std::forward<U>(u), std::forward<T>(t));
};

概念 destructible

template<class T>
concept destructible = is_nothrow_destructible_v<T>;

概念 constructible_from

template<class T, class... Args>
concept constructible_from = destructible<T> && is_constructible_v<T, Args...>;

概念 default_initializable

template<class T>
constexpr bool /*is-default-initializable*/ = /* see description */; // exposition only
 
template<class T>
concept default_initializable =
  constructible_from<T> && requires { T{}; } && /*is-default-initializable*/<T>;

概念 move_constructible

template<class T>
concept move_constructible = constructible_from<T, T> && convertible_to<T, T>;

概念 copy_constructible

template<class T>
concept copy_constructible =
  move_constructible<T> && constructible_from<T, T&> && convertible_to<T&, T> &&
  constructible_from<T, const T&> && convertible_to<const T&, T> &&
  constructible_from<T, const T> && convertible_to<const T, T>;

概念 equality_comparable

template<class T, class U>
concept /*weakly-equality-comparable-with*/ = // exposition only
  requires(const remove_reference_t<T>& t, const remove_reference_t<U>& u) {
    { t == u } -> boolean-testable;
    { t != u } -> boolean-testable;
    { u == t } -> boolean-testable;
    { u != t } -> boolean-testable;
  };
 
template<class T>
concept equality_comparable = /*weakly-equality-comparable-with*/<T, T>;

概念 equality_comparable_with

template<class T, class U, class C = common_reference_t<const T&, const U&>>
concept /*comparison-common-type-with-impl*/ = // exposition only
  same_as<common_reference_t<const T&, const U&>,
          common_reference_t<const U&, const T&>> &&
  requires {
    requires convertible_to<const T&, const C&> || convertible_to<T, const C&>;
    requires convertible_to<const U&, const C&> || convertible_to<U, const C&>;
  };
 
template<class T, class U>
concept /*comparison-common-type-with*/ = // exposition only
  /*comparison-common-type-with-impl*/<remove_cvref_t<T>, remove_cvref_t<U>>;
 
template<class T, class U>
concept equality_comparable_with =
  equality_comparable<T> && equality_comparable<U> &&
  /*comparison-common-type-with*/<T, U> &&
  equality_comparable<
    common_reference_t<const remove_reference_t<T>&, const remove_reference_t<U>&>> &&
  /*weakly-equality-comparable-with*/<T, U>;

辅助概念 partially-ordered-with

定义在头文件 <compare> 中

template<class T, class U>
concept /*partially-ordered-with*/ = // exposition only
  requires(const remove_reference_t<T>& t, const remove_reference_t<U>& u) {
    { t <  u } -> boolean-testable;
    { t >  u } -> boolean-testable;
    { t <= u } -> boolean-testable;
    { t >= u } -> boolean-testable;
    { u <  t } -> boolean-testable;
    { u >  t } -> boolean-testable;
    { u <= t } -> boolean-testable;
    { u >= t } -> boolean-testable;
  };

概念 totally_ordered

template<class T>
concept totally_ordered = equality_comparable<T> && /*partially-ordered-with*/<T, T>;

概念 totally_ordered_with

template<class T, class U>
concept totally_ordered_with =
  totally_ordered<T> && totally_ordered<U> && equality_comparable_with<T, U> &&
  totally_ordered<
    common_reference_t<const remove_reference_t<T>&, const remove_reference_t<U>&>> &&
  /*partially-ordered-with*/<T, U>;

概念 movable

template<class T>
concept movable =
  is_object_v<T> && move_constructible<T> && assignable_from<T&, T> && swappable<T>;

概念 copyable

template<class T>
concept copyable = copy_constructible<T> && movable<T> && assignable_from<T&, T&> &&
                   assignable_from<T&, const T&> && assignable_from<T&, const T>;

概念 semiregular

template<class T>
concept semiregular = copyable<T> && default_initializable<T>;

概念 regular

template<class T>
concept regular = semiregular<T> && equality_comparable<T>;

概念 invocable

template<class F, class... Args>
concept invocable = requires(F&& f, Args&&... args) {
  invoke(std::forward<F>(f),
         std::forward<Args>(args)...); // not required to be equality-preserving
};

概念 regular_invocable

template<class F, class... Args>
  concept regular_invocable = invocable<F, Args...>;

概念 predicate

template<class F, class... Args>
concept predicate =
  regular_invocable<F, Args...> && boolean-testable<invoke_result_t<F, Args...>>;

概念 relation

template<class R, class T, class U>
concept relation =
  predicate<R, T, T> && predicate<R, U, U> && predicate<R, T, U> && predicate<R, U, T>;

概念 equivalence_relation

template<class R, class T, class U>
concept equivalence_relation = relation<R, T, U>;

概念 strict_weak_order

template<class R, class T, class U>
concept strict_weak_order = relation<R, T, U>;