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7.1 Package Specifications and Declarations

A package is generally provided in two parts: a package_specification and a package_body. Every package has a package_specification, but not all packages have a package_body.
       package_declaration ::= package_specification;
       package_specification ::=
           package defining_program_unit_name is
           end [[parent_unit_name.]identifier]
Legality Rules
A package_declaration or generic_package_declaration requires a completion (a body) if it contains any declarative_item that requires a completion, but whose completion is not in its package_specification.
Static Semantics
The first list of declarative_items of a package_specification of a package other than a generic formal package is called the visible part of the package. The optional list of declarative_items after the reserved word private (of any package_specification) is called the private part of the package. If the reserved word private does not appear, the package has an implicit empty private part.
An entity declared in the private part of a package is visible only within the declarative region of the package itself (including any child units -- see 10.1.1). In contrast, expanded names denoting entities declared in the visible part can be used even outside the package; furthermore, direct visibility of such entities can be achieved by means of use_clauses (see 4.1.3 and 8.4).
Dynamic Semantics
The elaboration of a package_declaration consists of the elaboration of its basic_declarative_items in the given order.

Example of a package declaration:
       package Rational_Numbers is
          type Rational is
                Numerator   : Integer;
                Denominator : Positive;
             end record;
          function "="(X,Y : Rational) return Boolean;
          function "/"  (X,Y : Integer)  return Rational;  --  to construct a rational number
          function "+"  (X,Y : Rational) return Rational;
          function "-"  (X,Y : Rational) return Rational;
          function "*"  (X,Y : Rational) return Rational;
          function "/"  (X,Y : Rational) return Rational;
       end Rational_Numbers;
There are also many examples of package declarations in the predefined language environment (see Annex A).

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