20 General utilities library [utilities]

20.14 Function objects [function.objects]

20.14.15 Function object binders [func.bind] Class template is_­bind_­expression [func.bind.isbind]

namespace std { template<class T> struct is_bind_expression; // see below }
The class template is_­bind_­expression can be used to detect function objects generated by bind.
The function template bind uses is_­bind_­expression to detect subexpressions.
Specializations of the is_­bind_­expression template shall meet the Cpp17UnaryTypeTrait requirements ([meta.rqmts]).
The implementation provides a definition that has a base characteristic of true_­type if T is a type returned from bind, otherwise it has a base characteristic of false_­type.
A program may specialize this template for a program-defined type T to have a base characteristic of true_­type to indicate that T should be treated as a subexpression in a bind call.