std::ranges:: iter_swap

Swaps values denoted by two iterators.

The effect of the exposition-only helper function iter-exchange-move is equivalent to

std::iter_value_t<X> old(std::ranges::iter_move(x));
*x = std::ranges::iter_move(y);
return old;

ranges :: iter_swap ( i1, i2 ) is expression-equivalent to:

1. ( void ) iter_swap ( i1, i2 ) , if i1 or i2 has a class or enumeration type and the expression is well-formed, where the overload resolution of iter_swap is performed with the additional candidate void iter_swap ( auto , auto ) = delete ; ^[1] , excluding std::ranges::iter_swap itself.
   • If the selected overload does not exchange the value denoted by i1 and i2 , the program is ill-formed, no diagnostic required.
2. Otherwise, ranges:: swap ( * i1, * i2 ) if both I1 and I2 model indirectly_readable and if std:: iter_reference_t < I1 > and std:: iter_reference_t < I2 > model swappable_with .
3. Otherwise, ( void ) ( * i1 = iter-exchange-move ( i2, i1 ) ) , if std:: indirectly_movable_storable < I1, I2 > and std:: indirectly_movable_storable < I2, I1 > are both modeled, except that i1 is only evaluated once.
4. Otherwise, ranges :: iter_swap ( i1, i2 ) is ill-formed, which can result in substitution failure when ranges :: iter_swap ( i1, i2 ) appears in the immediate context of a template instantiation.

1. ↑ This precludes calling unconstrained std::iter_swap .

Customization point objects

The name ranges::iter_swap denotes a customization point object , which is a const function object of a literal semiregular class type. For exposition purposes, the cv-unqualified version of its type is denoted as __iter_swap_fn .

All instances of __iter_swap_fn are equal. The effects of invoking different instances of type __iter_swap_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, ranges::iter_swap can be copied freely and its copies can be used interchangeably.

Given a set of types Args... , if std:: declval < Args > ( ) ... meet the requirements for arguments to ranges::iter_swap above, __iter_swap_fn models

• std:: invocable < __iter_swap_fn, Args... > ,
• std:: invocable < const __iter_swap_fn, Args... > ,
• std:: invocable < __iter_swap_fn & , Args... > , and
• std:: invocable < const __iter_swap_fn & , Args... > .
  

Otherwise, no function call operator of __iter_swap_fn participates in overload resolution.

Example

See also