8 Visibility Rules
[The rules defining the scope of declarations and the rules defining
are visible at (or from) various places in the text of the program are
described in this clause. The formulation of these rules uses the notion
of a declarative region.
As explained in Clause 3
, a declaration declares
a view of an entity and associates a defining name with that view. The
view comprises an identification of the viewed entity, and possibly additional
properties. A usage name denotes a declaration. It also denotes the view
declared by that declaration, and denotes the entity of that view. Thus,
two different usage names might denote two different views of the same
entity; in this case they denote the same entity.]
To be honest: In some cases, a usage
name that denotes a declaration does not denote the view declared by
that declaration, nor the entity of that view, but instead denotes a
view of the current instance of the entity, and denotes the current instance
of the entity. This sometimes happens when the usage name occurs inside
the declarative region of the declaration.
Wording Changes from Ada 83
We no longer define the term “basic operation;”
thus we no longer have to worry about the visibility of them. Since they
were essentially always visible in Ada 83, this change has no effect.
The reason for this change is that the definition in Ada 83 was confusing,
and not quite correct, and we found it difficult to fix. For example,
one wonders why an if_statement
was not a basic operation of type Boolean. For another example, one wonders
what it meant for a basic operation to be “inherent in” something.
Finally, this fixes the problem addressed by AI83-00027/07.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe