Ada Reference Manual (Ada 2022) — Legal Information

6.7 Null Procedures

1/2

A null_procedure_declaration provides a shorthand to declare a procedure with an empty body.

Syntax

2/3

null_procedure_declaration ::=
   [overriding_indicator]
   procedure_specification is null
       [aspect_specification];

Legality Rules

2.1/3

If a null_procedure_declaration is a completion, it shall be the completion of a subprogram_declaration or generic_subprogram_declaration. The profile of a null_procedure_declaration that completes a declaration shall conform fully to that of the declaration.

Static Semantics

3/5

A null_procedure_declaration that is not a completion declares a null procedure. A completion is not allowed for a null_procedure_declaration; however, a null_procedure_declaration can complete a previous declaration.

Dynamic Semantics

4/5

The execution of a null procedure is invoked by a subprogram call. For the execution of a subprogram call on a null procedure, or on a procedure completed with a null_procedure_declaration, the execution of the subprogram_body has no effect.

5/3

The elaboration of a null_procedure_declaration has no other effect than to establish that the null procedure can be called without failing the Elaboration_Check.

Examples

6/5

Example of the declaration of a null procedure:

7/5

procedure Simplify(Expr : in out Expression) is null; -- see 3.9
-- By default, Simplify does nothing, but it can be overridden in extensions of Expression

Ada 2005 and 2012 Editions sponsored in part by Ada-Europe