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. See CustomizationPointObject for details.

[edit] Example

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