Template:cpp/experimental/ranges/cpo

Customization point objects
The name denotes a customization point object, which is a function object of a literal  class type (denoted, for exposition purposes, as ). All instances of are equal. Thus, can be copied freely and its copies can be used interchangeably.

Given a set of types, if meet the requirements for arguments to  above,  will satisfy. Otherwise, no function call operator of participates in overload resolution.

In every translation unit in which is defined, it refers to the same instance of the customization point object. (This means that it can be used freely in things like inline functions and function templates without violating the one-definition rule.)