13.9.2 The Valid Attribute
The Valid attribute can be used to check the validity of data produced by unchecked conversion, input, interface to foreign languages, and the like.
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,
- 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.
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Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual