NAME¶

std::ranges::iter_move - std::ranges::iter_move

Synopsis¶

Defined in header <iterator>
inline namespace /*unspecified*/ {

inline constexpr /*unspecified*/ iter_move = (since C++20)
/*unspecified*/; (customization point object)

}
Call signature
template< class T >

requires /* see below */

constexpr decltype(auto) iter_move( T&& t )
noexcept(/* see below */);

Obtains an rvalue reference or a prvalue temporary from a given iterator.

A call to ranges::iter_move is expression-equivalent to:

1. iter_move(std::forward<T>(t)), if std::remove_cvref_t<T> is a class or
enumeration type and the expression is well-formed in unevaluated context, where
the overload resolution is performed with the following candidates:

* void iter_move();
* any declarations of iter_move found by argument-dependent lookup.

2. Otherwise, std::move(*std::forward<T>(t)) if *std::forward<T>(t) is well-formed
and is an lvalue.
3. Otherwise, *std::forward<T>(t) if *std::forward<T>(t) is well-formed and is an

rvalue.¶

In all other cases, a call to ranges::iter_move is ill-formed, which can result in
substitution failure when ranges::iter_move(e) appears in the immediate context of a
template instantiation.

If ranges::iter_move(e) is not equal to *e, the program is ill-formed, no diagnostic
required.

Expression-equivalent

Expression e is expression-equivalent to expression f, if

* e and f have the same effects, and
* either both are constant subexpressions or else neither is a constant
subexpression, and
* either both are potentially-throwing or else neither is potentially-throwing
(i.e. noexcept(e) == noexcept(f)).

Customization point objects

The name ranges::iter_move 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_move_fn.

All instances of __iter_move_fn are equal. The effects of invoking different
instances of type __iter_move_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_move 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_move above, __iter_move_fn models

* std::invocable<__iter_move_fn, Args...>,
* std::invocable<const __iter_move_fn, Args...>,
* std::invocable<__iter_move_fn&, Args...>, and
* std::invocable<const __iter_move_fn&, Args...>.

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

See also¶

iter_move casts the result of dereferencing the adjusted underlying iterator to its
(C++20) associated rvalue reference type
(function)
iter_move casts the result of dereferencing the underlying iterator to its
(C++20) associated rvalue reference type
(function)