20 General utilities library [utilities]

20.15 Metaprogramming and type traits [meta]

20.15.5 Unary type traits [meta.unary] General [meta.unary.general]

Subclause [meta.unary] contains templates that may be used to query the properties of a type at compile time.
Each of these templates shall be a Cpp17UnaryTypeTrait ([meta.rqmts]) with a base characteristic of true_­type if the corresponding condition is true, otherwise false_­type.