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3.11.1 Completions of Declarations

Declarations sometimes come in two parts. A declaration that requires a second part is said to require completion. The second part is called the completion of the declaration (and of the entity declared), and is either another declaration, a body, or a pragma. A body is a body, an entry_body, or a renaming-as-body (see 8.5.4). 

Name Resolution Rules

A construct that can be a completion is interpreted as the completion of a prior declaration only if: 

Legality Rules

An implicit declaration shall not have a completion. For any explicit declaration that is specified to require completion, there shall be a corresponding explicit completion.
At most one completion is allowed for a given declaration. Additional requirements on completions appear where each kind of completion is defined. 
A type is completely defined at a place that is after its full type definition (if it has one) and after all of its subcomponent types are completely defined. A type shall be completely defined before it is frozen (see 13.14 and 7.3). 
91  Completions are in principle allowed for any kind of explicit declaration. However, for some kinds of declaration, the only allowed completion is a pragma Import, and implementations are not required to support pragma Import for every kind of entity. 
92  There are rules that prevent premature uses of declarations that have a corresponding completion. The Elaboration_Checks of 3.11 prevent such uses at run time for subprograms, protected operations, tasks, and generic units. The rules of 13.14, “Freezing Rules” prevent, at compile time, premature uses of other entities such as private types and deferred constants. 

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