std::swappable,std::swappable_with(3) | C++ Standard Libary | std::swappable,std::swappable_with(3) |

# NAME¶

std::swappable,std::swappable_with - std::swappable,std::swappable_with

# Synopsis¶

Defined in header <concepts>

template< class T >

concept swappable =

requires(T& a, T& b) { **(1)** *(since C++20)*

ranges::swap(a, b);

};

template< class T, class U >

concept swappable_with =

std::common_reference_with<T, U> &&

requires(T&& t, U&& u) {

ranges::swap(std::forward<T>(t), std::forward<T>(t)); **(2)**
*(since C++20)*

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));

};

The concept swappable<T> specifies that lvalues of type T are
swappable.

The concept swappable_with<T, U> specifies that expressions of the type
and value

category encoded by T and U are swappable with each other.
swappable_with<T, U> is

satisfied only if a call to ranges::swap(t, u) exchanges the value of t and
u, that

is, given distinct objects t2 equal to t and u2 equal to u, after evaluating
either

ranges::swap(t, u) or ranges::swap(u, t), t2 is equal to u and u2 is equal to
t.

Equality preservation

An expression is equality preserving if it results in equal outputs given
equal

inputs.

* The inputs to an expression consist of its operands.

* The outputs of an expression consist of its result and all operands
modified by

the expression (if any).

In specification of standard concepts, operands are defined as the largest

subexpressions that include only:

* an id-expression, and

* invocations of std::move, std::forward, and std::declval.

The cv-qualification and value category of each operand is determined by
assuming

that each template type parameter denotes a cv-unqualified complete non-array
object

type.

Every expression required to be equality preserving is further required to be

stable: two evaluations of such an expression with the same input objects
must have

equal outputs absent any explicit intervening modification of those input
objects.

Unless noted otherwise, every expression used in a requires-expression is
required

to be equality preserving and stable, and the evaluation of the expression
may

modify only its non-constant operands. Operands that are constant must not be

modified.

2022.07.31 | http://cppreference.com |