std::is_copy_assignable, std::is_trivially_copy_assignable, std::is_nothrow_copy_assignable

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C++
 
实用工具库
类型的支持 (basic types, RTTI, type traits)
动态内存管理
错误处理
程序实用工具
可变参数函数
日期和时间
函数对象
initializer_list（C++11）
bitset
hash（C++11）
关系运算符
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Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
双和元组
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Pairs and tuples
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pair
tuple（C++11）
piecewise_construct_t（C++11）
piecewise_construct（C++11）
掉期，远期和移动
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Swap, forward and move
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swap
forward（C++11）
move（C++11）
move_if_noexcept（C++11）
declval（C++11）
 
类型的支持
基本类型
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Basic types
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基本类型
固定宽度的整数类型 （C++11）
nullptr_t（C++11）
offsetof
NULL
数值范围内
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Numeric limits
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numeric_limits
C数字限制接口
运行时类型信息
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Runtime type information
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type_info
type_index（C++11）
类型特征
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Type traits
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初级型两类
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Primary type categories
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is_void（C++11）
is_array（C++11）
is_pointer（C++11）
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is_union（C++11）
is_class（C++11）
is_function（C++11）
is_object（C++11）
is_scalar（C++11）
is_compound（C++11）
is_integral（C++11）
is_floating_point（C++11）
is_fundamental（C++11）
is_arithmetic（C++11）
is_reference（C++11）
is_lvalue_reference（C++11）
is_rvalue_reference（C++11）
is_member_pointer（C++11）
is_member_object_pointer（C++11）
is_member_function_pointer（C++11）
类型属性
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Type properties
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is_const（C++11）
is_volatile（C++11）
is_pod（C++11）
is_empty（C++11）
is_polymorphic（C++11）
is_abstract（C++11）
is_trivial（C++11）
is_trivially_copyable（C++11）
is_standard_layout（C++11）
is_literal_type（C++11）
is_signed（C++11）
is_unsigned（C++11）
支持的操作
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Supported operations
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is_constructible
is_trivially_constructible
is_nothrow_constructible		（C++11）
（C++11）
（C++11）
is_default_constructible
is_trivially_default_constructible
is_nothrow_default_constructible		（C++11）
（C++11）
（C++11）
is_copy_constructible
is_trivially_copy_constructible
is_nothrow_copy_constructible		（C++11）
（C++11）
（C++11）
is_move_constructible
is_trivially_move_constructible
is_nothrow_move_constructible		（C++11）
（C++11）
（C++11）
is_assignable
is_trivially_assignable
is_nothrow_assignable		（C++11）
（C++11）
（C++11）
is_copy_assignable
is_trivially_copy_assignable
is_nothrow_copy_assignable		（C++11）
（C++11）
（C++11）
is_move_assignable
is_trivially_move_assignable
is_nothrow_move_assignable		（C++11）
（C++11）
（C++11）
is_destructible
is_trivially_destructible
is_nothrow_destructible		（C++11）
（C++11）
（C++11）
has_virtual_destructor（C++11）
关系和属性查询
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Relationships and property queries
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is_same（C++11）
is_base_of（C++11）
is_convertible（C++11）
alignment_of（C++11）
rank（C++11）
extent（C++11）
类型的修改
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Type modifications
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remove_cv
remove_const
remove_volatile		（C++11）
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（C++11）
add_cv
add_const
add_volatile		（C++11）
（C++11）
（C++11）
make_signed（C++11）
make_unsigned（C++11）
remove_reference（C++11）
add_lvalue_reference
add_rvalue_reference		（C++11）
（C++11）
remove_pointer（C++11）
add_pointer（C++11）
remove_extent（C++11）
remove_all_extents（C++11）
类型转换
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Type transformations
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aligned_storage（C++11）
aligned_union（C++11）
decay（C++11）
enable_if（C++11）
conditional（C++11）
common_type（C++11）
underlying_type（C++11）
result_of（C++11）
键入特征常数
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Type trait constants
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integral_constant（C++11）
 
Defined in header <type_traits>
template< class T >
struct is_copy_assignable;
 (1) （C++11 起）
template< class T >
struct is_trivially_copy_assignable;
 (2) （C++11 起）
template< class T >
struct is_nothrow_copy_assignable;
 (3) （C++11 起）
1)
检查一个类型是否是CopyAssignable，即有一个可访问的显式或隐式的拷贝赋值运算符。如果符合要求，一个成员value等于true，否则value是false.
Original:
Checks whether a type is CopyAssignable, i.e. has an accessible explicit or implicit copy assignment operator. If the requirement is met, a member constant value equal true is provided, otherwise value is false.
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2)
同为1），但评价的拷贝赋值表达式不会调用任何操作，是不平凡的.
Original:
Same as 1), but evaluation of the copy-assignment expression will not call any operation that is not trivial.
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3)
同为1），但评价的拷贝赋值表达式的不叫任何​​操作，不noexcept的.
Original:
Same as 1), but the evaluation of the copy-assignment expression will not call any operation that is not noexcept.
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目录

Inherited from std::integral_constant

Member constants

value
[静态的] </ SPAN></div></div>
true如果 T is copy-assignable，false其他方式
Original:
true if T is copy-assignable, false otherwise
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（公共静态成员常量）

Member functions

operator bool
转换的对象bool，返回value
Original:
converts the object to bool, returns value
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（公共成员函数）

Member types

类型
Original:
Type
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 Definition
value_type bool
type std::integral_constant<bool, value>

</div>

[编辑] 可能的实现

template< class T>
struct is_copy_assignable
    : std::is_assignable< typename std::add_lvalue_reference<T>::type,
                    const typename std::add_lvalue_reference<T>::type> {};
 
template< class T>
struct is_trivially_copy_assignable
    : std::is_trivially_assignable< typename std::add_lvalue_reference<T>::type,
                              const typename std::add_lvalue_reference<T>::type> {};
 
template< class T>
struct is_nothrow_copy_assignable
    : std::is_nothrow_assignable< typename std::add_lvalue_reference<T>::type,
                            const typename std::add_lvalue_reference<T>::type> {};

[编辑] 为例

#include <iostream>
#include <utility>
#include <type_traits>
struct Foo { int n; };
int main() {
    std::cout << std::boolalpha
              << "Foo is trivally copy-assignable? "
              << std::is_trivially_copy_assignable<Foo>::value << '\n'
              << "int[2] is copy-assignable? "
              << std::is_copy_assignable<int[2]>::value << '\n'
              << "int is nothrow copy-assignable? "
              << std::is_nothrow_copy_assignable<int>::value << '\n';
}

Output: 

Foo is trivally copy-assignable? true
int[2] is copy-assignable? false
int is nothrow copy-assignable? true

[编辑] 另请参阅

（C++11）
（C++11）
（C++11）
如果一个类型的检查有特定参数的赋​​值操作符
Original:
checks if a type has a assignment operator for a specific argument
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（类模板） [edit]
（C++11）
（C++11）
（C++11）
一类的检查，如果有一招赋值运算符
Original:
checks if a type has a move assignment operator
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（类模板） [edit]
来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/types/is_copy_assignable&oldid=27517”