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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.
data can be created in the following cases (not counting erroneous or
- an uninitialized
- the result of
an unchecked conversion,
- interface to
another language (including machine code),
- disrupting an
assignment due to the failure of a language-defined check (see 11.6),
- 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
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