Ada 2012 Reference Manual

J.15.6 Pragma Unchecked_Union

The form of a pragma Unchecked_Union, which is a representation pragma (see 13.1), is as follows:

pragma Unchecked_Union (first_subtype_local_name);

The first_subtype_local_name of a pragma Unchecked_Union shall denote an unconstrained discriminated record subtype having a variant_part.

A pragma Unchecked_Union specifies that the Unchecked_Union aspect (see B.3.3) for the type denoted by first_subtype_local_name has the value True.