std::ranges::iter_move

 

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ranges::iter_move (C++20)
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Defined in header <iterator>
inline namespace /*unspecified*/ {     inline constexpr /*unspecified*/ iter_move = /*unspecified*/; }		(since C++20) (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 (C++20)	casts the result of dereferencing the adjusted underlying iterator to its associated rvalue reference type (function)
iter_move (C++20)	casts the result of dereferencing the underlying iterator to its associated rvalue reference type (function)