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std::ranges::iter_move

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< cpp‎ | iterator
 
 
Iterator library
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(C++20)
Iterator adaptors
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ranges::iter_move
(C++20)
Iterator operations
(C++11)
(C++11)
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(C++11)(C++14)
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(C++17)
(C++17)
 
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:
  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.

[edit] Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

[edit] 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.

[edit] See also

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