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8.4 Use Clauses

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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

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use_clause ::= use_package_clause | use_type_clause
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use_package_clause ::= use package_name {, package_name};
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use_type_clause ::= use type subtype_mark {, subtype_mark};

Legality Rules

5/2
A package_name of a use_package_clause shall denote a nonlimited view of a package. 

Static Semantics

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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.
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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. 
7.1/2
  A package is named in a use_package_clause if it is denoted by a package_name of that clause. A type is named in a use_type_clause if it is determined by a subtype_mark of that clause.
8/2
For each package named in 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 named in 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. 
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A declaration is use-visible if it is potentially use-visible, except in these naming-conflict cases: 
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Dynamic Semantics

12
The elaboration of a use_clause has no effect. 

Examples

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Example of a use clause in a context clause: 
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with Ada.Calendar; use Ada;
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Example of a use type clause: 
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use type Rational_Numbers.Rational; -- see 7.1
Two_Thirds: Rational_Numbers.Rational := 2/3;

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