10.1.6 Environment-Level Visibility Rules
1
[The normal visibility rules do not apply within
a parent_unit_name or a context_clause,
nor within a pragma that appears at the place
of a compilation unit. The special visibility rules for those contexts
are given here.]
Static Semantics
2/2
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{directly visible (within the parent_unit_name
of a library unit) [partial]} {visible
(within the parent_unit_name of a library unit) [partial]}
{directly visible
(within a with_clause) [partial]} {visible
(within a with_clause) [partial]} Within
the
parent_unit_name at the beginning of
an
explicit a library_item,
and within a
nonlimited_with_clause with_clause,
the only declarations that are visible are those that are
explicit library_items of the environment,
and the only declarations that are directly visible are those that are
explicit root
library_items of the
environment.
Within a limited_with_clause,
the only declarations that are visible are those that are the implicit
declaration of the limited view of a library package of the environment,
and the only declarations that are directly visible are those that are
the implicit declaration of the limited view of a root library package. {notwithstanding}
Notwithstanding the rules of 4.1.3,
an expanded name in a with_clause may consist
of a prefix that denotes a generic package
and a selector_name that denotes a child of
that generic package. [(The child is necessarily a generic unit; see
10.1.1.)]2.a
Ramification: In “package
P.Q.R is ... end P.Q.R;”, this rule requires P to
be a root library unit, and Q to be a library unit (because those are
the things that are directly visible and visible). Note that visibility
does not apply between the “end” and the “;”.
2.b
Physically nested declarations are not visible
at these places.
2.c
Although Standard is visible at these places,
it is impossible to name it, since it is not directly visible, and it
has no parent.
2.c.1/2
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Only compilation units defining limited views can
be mentioned in a limited_with_clause, while
only compilation units defining full views (that is, the explicit declarations)
can be mentioned in a nonlimited_with_clause.
This resolves the conflict inherent in having two compilation units with
the same defining name. 2.d/2
This paragraph
was deleted.Reason: {
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The “notwithstanding” part allows “with
A.B;” where A is a generic library package and B is one of its
(generic) children. This is necessary because it is not normally legal
to use an expanded name to reach inside a generic package.
3
{directly visible
(within a use_clause in a context_clause) [partial]} {visible
(within a use_clause in a context_clause) [partial]} {directly
visible (within a pragma in a context_clause) [partial]}
{visible (within
a pragma in a context_clause) [partial]} Within
a
use_clause or
pragma
that is within a
context_clause, each
library_item
mentioned in a previous
with_clause of the
same
context_clause is visible, and each root
library_item so mentioned is directly visible.
In addition, within such a
use_clause, if
a given declaration is visible or directly visible, each declaration
that occurs immediately within the given declaration's visible part is
also visible. No other declarations are visible or directly visible.
3.a
Discussion: Note the word “same”.
For example, if a with_clause on a declaration
mentions X, this does not make X visible in use_clauses
and pragmas that are on the body. The reason
for this rule is the one-pass context_clauses
Language Design Principle.
3.b
Note that the second part of the rule does not
mention pragmas.
4
{directly visible
(within the parent_unit_name of a subunit) [partial]} {visible
(within the parent_unit_name of a subunit) [partial]} Within
the
parent_unit_name of a subunit,
library_items
are visible as they are in the
parent_unit_name
of a
library_item; in addition, the declaration
corresponding to each
body_stub in the environment
is also visible.
4.a
Ramification: For a subprogram without
a separate subprogram_declaration, the body_stub
itself is the declaration.
5
{directly visible
(within a pragma that appears at the place of a compilation unit)
[partial]} {visible
(within a pragma that appears at the place of a compilation unit)
[partial]} Within a
pragma
that appears at the place of a compilation unit, the immediately preceding
library_item and each of its ancestors is
visible. The ancestor root
library_item is
directly visible.
6/2
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{notwithstanding}
Notwithstanding the rules of 4.1.3,
an expanded name in a with_clause, a pragma
in a context_clause, or a pragma
that appears at the place of a compilation unit may consist of a prefix
that denotes a generic package and a selector_name
that denotes a child of that generic package. [(The child is necessarily
a generic unit; see 10.1.1.)] 6.a/2
Reason: This rule
allows with A.B; and pragma Elaborate(A.B); where A is
a generic library package and B is one of its (generic) children. This
is necessary because it is not normally legal to use an expanded name
to reach inside a generic package.
Wording Changes from Ada 83
6.b
The special visibility rules that apply within
a parent_unit_name or a context_clause,
and within a pragma that appears at the place
of a compilation_unit are clarified.
6.c
Note that a context_clause
is not part of any declarative region.
6.d
We considered making the visibility rules within
parent_unit_names and context_clauses
follow from the context of compilation. However, this attempt failed
for various reasons. For example, it would require use_clauses
in context_clauses to be within the declarative
region of Standard, which sounds suspiciously like a kludge. And we would
still need a special rule to prevent seeing things (in our own context_clause)
that were with-ed by our parent, etc.
Wording Changes from Ada 95
6.e/2
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Added separate visibility rules for limited_with_clauses;
the existing rules apply only to nonlimited_with_clauses.6.f/2
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Clarified that the name of a generic child unit
may appear in a pragma in a context_clause.
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