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Customization point object

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Ranges library
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(C++23)

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[edit] Explanation

The name ranges::cpo 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 __cpo_fn.

All instances of __cpo_fn are equal. The effects of invoking different instances of type __cpo_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::cpo 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::cpo above, __cpo_fn models

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

[edit] See also