cpp/utility/functional/placeholders

The std namespace contains the placeholder objects where  is an implementation defined maximum number.

When used as an argument in a std expression, the placeholder objects are stored in the generated function object, and when that function object is invoked with unbound arguments, each placeholder is replaced by the corresponding Nth unbound argument.

The types of the placeholder objects are and, their default copy/move constructors do not throw exceptions, and for any placeholder , the type  is defined, where  is derived from.