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8.4 Use Clauses
1
A use_package_clause
achieves direct visibility of declarations that appear in the visible
part of a package; a use_type_clause
achieves direct visibility of the primitive operators of a type.
Syntax
2
use_clause
::= use_package_clause |
use_type_clause
3
use_package_clause
::= use package_name {,
package_name};
4
use_type_clause
::= use type subtype_mark {,
subtype_mark};
Legality Rules
5
A package_name
of a use_package_clause shall denote
a package.
Static Semantics
6
For each
use_clause,
there is a certain region of text called the
scope of the
use_clause.
For a
use_clause within a
context_clause
of a
library_unit_declaration or
library_unit_renaming_declaration,
the scope is the entire declarative region of the declaration. For a
use_clause within a
context_clause
of a body, the scope is the entire body and any subunits (including multiply
nested subunits). The scope does not include
context_clauses
themselves.
7
For a use_clause
immediately within a declarative region, the scope is the portion of
the declarative region starting just after the use_clause
and extending to the end of the declarative region. However, the scope
of a use_clause in the private part
of a library unit does not include the visible part of any public descendant
of that library unit.
8
For each package denoted by
a
package_name of a
use_package_clause
whose scope encloses a place, each declaration that occurs immediately
within the declarative region of the package is
potentially use-visible
at this place if the declaration is visible at this place. For each type
T or
T'Class determined by a
subtype_mark
of a
use_type_clause whose scope
encloses a place, the declaration of each primitive operator of type
T is potentially use-visible at this place if its declaration
is visible at this place.
9
A
declaration is
use-visible if it is potentially use-visible, except
in these naming-conflict cases:
10
- A potentially use-visible declaration
is not use-visible if the place considered is within the immediate scope
of a homograph of the declaration.
11
- Potentially use-visible declarations
that have the same identifier are
not use-visible unless each of them is an overloadable declaration.
Dynamic Semantics
12
The elaboration of a
use_clause
has no effect.
Examples
13
Example of a
use clause in a context clause:
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with Ada.Calendar; use Ada;
15
Example of a use
type clause:
16
use type Rational_Numbers.Rational; -- see 7.1
Two_Thirds: Rational_Numbers.Rational := 2/3;
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