C++函数对象-运算符函数对象 - 位运算 - 实现 x y 的函数对象（std::bit

任何定义了函数调用操作符的对象都是函数对象。C++ 支持创建、操作新的函数对象，同时也提供了许多内置的函数对象。

运算符函数对象

C++ 针对常用的算术和逻辑运算定义了很多函数对象：

位运算

实现 x & y 的函数对象

std::bit_and

template< class T > struct bit_and;		(C++14 前)
template< class T = void > struct bit_and;		(C++14 起)

进行逐位与的函数对象。等效地调用类型 T 上的 operator& 。

特化

标准库提供 std::bit_and 在不指定 T 时的特化，它使得参数类型和返回类型留待推导。

bit_and<void>

实现 x & y 并推导参数和返回类型的函数对象
(类模板特化)

(C++14 起)

成员类型

类型	定义
`result_type`(C++17 中弃用)	`T`
`first_argument_type`(C++17 中弃用)	`T`
`second_argument_type`(C++17 中弃用)	`T`

(C++20 前)

成员函数

operator()

返回二个参数逐位与的结果
(公开成员函数)

std::bit_and::operator()

T operator()( const T& lhs, const T& rhs ) const;		(C++14 前)
constexpr T operator()( const T& lhs, const T& rhs ) const;		(C++14 起)

返回 lhs 和 rhs 逐位与的结果。

参数

lhs, rhs

要计算逐位与的值

返回值

lhs & rhs 的结果。

异常

（无）

可能的实现

constexpr T operator()(const T &lhs, const T &rhs) const 
{return lhs & rhs;
}

std::bit_and<void>

std::bit_and<void>

template<>
class bit_and<void>;

(C++14 起)

std::bit_and<> 是 std::bit_and 的特化，拥有推导出的参数和返回类型。

成员类型

成员类型	定义
`is_transparent`	/* 未指定 */

成员函数

operator()

应用 operator& 到 lhs 和 rhs
(公开成员函数)

std::bit_and<>::operator()

template< class T, class U>

constexpr auto operator()( T&& lhs, U&& rhs ) const

-> decltype(std::forward<T>(lhs) & std::forward<U>(rhs));

返回 lhs & rhs 的结果。

参数

lhs, rhs

为之计算逐位与的值

返回值

lhs & rhs 的结果。

调用示例

#include <iostream>
#include <functional>struct Cell
{int x;int y;Cell() = default;Cell(int a, int b): x(a), y(b) {}Cell(const Cell &cell){x = cell.x;y = cell.y;}Cell &operator+(const Cell &cell){x += cell.x;y += cell.y;return *this;}Cell &operator+=(const Cell &cell){x += cell.x;y += cell.y;return *this;}Cell &operator*=(int n){x *= n;y *= n;return *this;}Cell &operator++(){x += 1;y += 1;return *this;}friend Cell operator +(const Cell &cell1, const Cell &cell2){Cell cell = cell1;cell += cell2;return cell;}friend Cell operator *(const Cell &cell1, const Cell &cell2){Cell cell = {cell1.x * cell2.x, cell1.y * cell2.y};return cell;}friend Cell operator /(const Cell &cell1, const Cell &cell2){Cell cell = {cell1.x / cell2.x, cell1.y / cell2.y};return cell;}friend Cell operator %(const Cell &cell1, const Cell &cell2){Cell cell = {cell1.x % cell2.x, cell1.y % cell2.y};return cell;}friend bool operator ==(const Cell &cell1, const Cell &cell2){return cell1.x == cell2.x && cell1.y == cell2.y;}friend bool operator !=(const Cell &cell1, const Cell &cell2){return cell1.x != cell2.x && cell1.y != cell2.y;}friend bool operator <(const Cell &cell1, const Cell &cell2){if (cell1.x == cell2.x){return cell1.y < cell2.y;}else{return cell1.x < cell2.x;}}friend bool operator >(const Cell &cell1, const Cell &cell2){if (cell1.x == cell2.x){return cell1.y > cell2.y;}else{return cell1.x > cell2.x;}}friend bool operator &&(const Cell &cell1, const Cell &cell2){return cell1.x && cell2.x && cell1.y && cell2.y;}friend bool operator ||(const Cell &cell1, const Cell &cell2){return cell1.x || cell2.x || cell1.y || cell2.y;}friend bool operator !(const Cell &cell){return !(cell.x && cell.x);}friend Cell operator &(const Cell &cell1, const Cell &cell2){Cell cell = {cell1.x & cell2.x, cell1.y & cell2.y};return cell;}friend Cell operator |(const Cell &cell1, const Cell &cell2){Cell cell = {cell1.x | cell2.x, cell1.y | cell2.y};return cell;}friend Cell operator ^(const Cell &cell1, const Cell &cell2){Cell cell = {cell1.x ^ cell2.x, cell1.y ^ cell2.y};return cell;}
};std::ostream &operator<<(std::ostream &os, const Cell &cell)
{os << "{" << cell.x << "," << cell.y << "}";return os;
}int main()
{std::cout << std::boolalpha;int *ptr = nullptr;
//    std::cout << "std::bit_and<int*>()(ptr, nullptr):      "
//              << std::bit_and<int*>()(ptr, nullptr) << std::endl;std::cout << "std::bit_and<char>()(50, 2):             "<< std::bit_and<char>()(50, 2) << std::endl;std::cout << "std::bit_and<char>()('a', 97):           "<< std::bit_and<char>()('a', 97) << std::endl;std::cout << "std::bit_and<int>()(1023, 1024):         "<< std::bit_and<int>()(1023, 1024) << std::endl;std::cout << "std::bit_and<long>()(1023, 1024):        "<< std::bit_and<long>()(1023, 1024) << std::endl;std::cout << "std::bit_and<long long>()(1023, 1024):   "<< std::bit_and<long long>()(1023, 1024) << std::endl;std::cout << "std::bit_and<uint8_t>()(1023, 1024):     "<< std::bit_and<uint8_t>()(8, 32) << std::endl;std::cout << "std::bit_and<uint16_t>()(123, 456):      "<< std::bit_and<uint16_t>()(123, 456) << std::endl;std::cout << "std::bit_and<uint32_t>()(101, 202):      "<< std::bit_and<uint32_t>()(101, 202) << std::endl;std::cout << "std::bit_and<uint64_t>()(10230, 10240):  "<< std::bit_and<uint64_t>()(10230, 10240) << std::endl;std::cout << "std::bit_and<int8_t>()(1023, 1024):      "<< std::bit_and<int8_t>()(8, 32) << std::endl;std::cout << "std::bit_and<int16_t>()(123, 456):       "<< std::bit_and<int16_t>()(123, 456) << std::endl;std::cout << "std::bit_and<int32_t>()(101, 202):       "<< std::bit_and<int32_t>()(101, 202) << std::endl;std::cout << "std::bit_and<int64_t>()(10230, 10240):   "<< std::bit_and<int64_t>()(10230, 10240) << std::endl;//    std::cout << "std::bit_and<double>()(3.14, 3.14):      "
//              << std::bit_and<double>()(3.14, 3.14) << std::endl;
//    std::cout << "std::bit_and<float>()(3.14, 3.14):       "
//              << std::bit_and<float>()(3.14, 3.14) << std::endl;
//    std::cout << "std::bit_and<float>()(3, 3):             "
//              << std::bit_and<float>()(3, 3) << std::endl;
//    std::cout << "std::bit_and<float>()(3.56, 3.14):       "
//              << std::bit_and<float>()(3.56, 3.14) << std::endl;
//    std::cout << "std::bit_and<int>()(3.14, 3.14):         "
//              << std::bit_and<int>()(3.34, 3.34) << std::endl;std::cout << "std::bit_and<Cell>()(Cell{101, 101}, Cell{202, 202}):       "<< std::bit_and<Cell>()(Cell{101, 101}, Cell{202, 202}) << std::endl;//编译失败
//    std::cout << "std::bit_and<std::string>()(\"I am a \", \"handsome programmer\"):"
//              << std::bit_and<std::string>()("I am a ", "handsome programmer") << std::endl;return 0;
}

输出

std::bit_and<char>()(50, 2):
std::bit_and<char>()('a', 97):           a
std::bit_and<int>()(1023, 1024):         0
std::bit_and<long>()(1023, 1024):        0
std::bit_and<long long>()(1023, 1024):   0
std::bit_and<uint8_t>()(1023, 1024):
std::bit_and<uint16_t>()(123, 456):      72
std::bit_and<uint32_t>()(101, 202):      64
std::bit_and<uint64_t>()(10230, 10240):  8192
std::bit_and<int8_t>()(1023, 1024):
std::bit_and<int16_t>()(123, 456):       72
std::bit_and<int32_t>()(101, 202):       64
std::bit_and<int64_t>()(10230, 10240):   8192
std::bit_and<Cell>()(Cell{101, 101}, Cell{202, 202}):       {64,64}