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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, a null_procedure_declaration or an expression_function_declaration that completes another declaration, 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: 
The declaration and the completion occur immediately within the same declarative region;
The defining name or defining_program_unit_name in the completion is the same as in the declaration, or in the case of a pragma, the pragma applies to the declaration;
If the declaration is overloadable, then the completion either has a type-conformant profile, or is a pragma.

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, unless the declared entity is imported (see B.1).
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). 
98  Completions are in principle allowed for any kind of explicit declaration. However, for some kinds of declaration, the only allowed completion is an implementation-defined pragma, and implementations are not required to have any such pragmas. 
99  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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