13.9.2 The Valid Attribute

From OC Systems Wiki!
Jump to: navigation, search

The Valid attribute can be used to check the validity of data produced by unchecked conversion, input, interface to foreign languages, and the like.

Static Semantics

For a prefix X that denotes a scalar object (after any implicit dereference), the following attribute is defined:

Yields True if and only if the object denoted by X is normal and has a valid representation. The value of this attribute is of the predefined type Boolean.


19  Invalid data can be created in the following cases (not counting erroneous or unpredictable execution):

  • an uninitialized scalar object,
  • the result of an unchecked conversion,
  • input,
  • interface to another language (including machine code),
  • aborting an assignment,
  • disrupting an assignment due to the failure of a language-defined check (see 11.6), and
  • use of an object whose Address has been specified.

20  X'Valid is not considered to be a read of X; hence, it is not an error to check the validity of invalid data.

Copyright © 1992,1993,1994,1995 Intermetrics, Inc.
Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual