std::exchange
cppreference.com
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template< class T, class U = T > T exchange( T& obj, U&& new_value ); |
( C++14) ( C++20) |
|
template< class T, class U = T > constexpr T exchange( T& obj, U&& new_value ); |
( C++20) ( C++23) |
|
template< class T, class U = T > constexpr T exchange( T& obj, U&& new_value ) noexcept(/* */); |
( C++23) | |
obj new_value obj.
| obj | , | |
| new_value | obj
| |
-T MoveConstructible. , - U T
| ||
obj
|
() |
( C++23) |
|
noexcept:
noexcept( std::is_nothrow_move_constructible_v<T> && std::is_nothrow_assignable_v<T&, U> ) |
( C++23) |
template<class T, class U = T>
constexpr // C++20
T exchange(T& obj, U&& new_value)
noexcept( // C++23
std::is_nothrow_move_constructible<T>::value &&
std::is_nothrow_assignable<T&, U>::value
)
{
T old_value = std::move(obj);
obj = std::forward<U>(new_value);
return old_value;
}
|
struct S
{
int n;
S(S&& other) noexcept : n{std::exchange(other.n, 0)}
{}
S& operator=(S&& other) noexcept
{
if (this != &other)
n = std::exchange(other.n, 0); // n, other.n
return *this;
}
};
__cpp_lib_exchange_function |
201304L |
(C++14) | std::exchange
|
#include <iostream>
#include <iterator>
#include <utility>
#include <vector>
class stream
{
public:
using flags_type = int;
public:
flags_type flags() const { return flags_; }
// flags_ newf .
flags_type flags(flags_type newf) { return std::exchange(flags_, newf); }
private:
flags_type flags_ = 0;
};
void f() { std::cout << "f()"; }
int main()
{
stream s;
std::cout << s.flags() << '\n';
std::cout << s.flags(12) << '\n';
std::cout << s.flags() << "\n\n";
std::vector<int> v;
// ,
//
// .
// std::exchange(v, std::vector<int>{1,2,3,4});
std::exchange(v, {1,2,3,4});
std::copy(begin(v), end(v), std::ostream_iterator<int>(std::cout,", "));
std::cout << "\n\n";
void (*fun)();
//
// .
// std::exchange(fun, static_cast<void(*)()>(f))
std::exchange(fun,f);
fun();
std::cout << "\n\n : ";
for (int a{0}, b{1}; a < 100; a = std::exchange(b, a + b))
std::cout << a << ", ";
std::cout << "...\n";
}
:
0
0
12
1, 2, 3, 4,
f()
: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
| ( ) | |
(C++11)(C++11) |
( ) |