tmp/tmp_cqnj6aw/{from.md → to.md}
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| 1 |
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#### `ranges::iter_swap` <a id="iterator.cust.swap">[[iterator.cust.swap]]</a>
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The name `ranges::iter_swap` denotes a customization point object
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[[customization.point.object]] that exchanges the values
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[[concept.swappable]] denoted by its arguments.
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Let *`iter-exchange-move`* be the exposition-only function:
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``` cpp
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template<class X, class Y>
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constexpr iter_value_t<X> iter-exchange-move(X&& x, Y&& y)
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noexcept(noexcept(iter_value_t<X>(iter_move(x))) &&
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noexcept(*x = iter_move(y)));
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```
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*Effects:* Equivalent to:
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``` cpp
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iter_value_t<X> old_value(iter_move(x));
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*x = iter_move(y);
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return old_value;
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```
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The expression `ranges::iter_swap(E1, E2)` for subexpressions `E1` and
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`E2` is expression-equivalent to:
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- `(void)iter_swap(E1, E2)`, if either `E1` or `E2` has class or
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enumeration type and `iter_swap(E1, E2)` is a well-formed expression
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with overload resolution performed in a context that includes the
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declaration
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``` cpp
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template<class I1, class I2>
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void iter_swap(I1, I2) = delete;
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```
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and does not include a declaration of `ranges::iter_swap`. If the
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function selected by overload resolution does not exchange the values
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denoted by `E1` and `E2`, the program is ill-formed, no diagnostic
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required.
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- Otherwise, if the types of `E1` and `E2` each model
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`indirectly_readable`, and if the reference types of `E1` and `E2`
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model `swappable_with` [[concept.swappable]], then
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`ranges::swap(*E1, *E2)`.
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- Otherwise, if the types `T1` and `T2` of `E1` and `E2` model
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`indirectly_movable_storable<T1, T2>` and
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`indirectly_movable_storable<T2, T1>`, then
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`(void)(*E1 = iter-exchange-move(E2, E1))`, except that `E1` is
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evaluated only once.
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- Otherwise, `ranges::iter_swap(E1, E2)` is ill-formed. \[*Note 1*: This
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case can result in substitution failure when
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`ranges::iter_swap(E1, E2)` appears in the immediate context of a
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template instantiation. — *end note*]
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