6.7 Null Procedures
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A null_procedure_declaration
provides a shorthand to declare a procedure with an empty body.
Syntax
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null_procedure_declaration ::=
[overriding_indicator]
procedure_specification is null;Static Semantics
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A null_procedure_declaration
declares a null procedure.{null
procedure} {procedure
(null)} A completion is not allowed for
a null_procedure_declaration. 3.a/2
Reason: There are
no null functions because the return value has to be constructed somehow;
a function that always raises Program_Error doesn't seem very useful
or worth the complication.
Dynamic Semantics
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The execution of a null procedure is invoked by
a subprogram call. For the execution of a subprogram call on a null procedure,
the execution of the subprogram_body has no
effect. 4.a/2
Ramification: Thus,
a null procedure is equivalent to the body
4.b/2
begin
null;
end;
4.c/2
with the exception that
a null procedure can be used in place of a procedure specification.
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{elaboration (null_procedure_declaration)
[partial]} The elaboration of a null_procedure_declaration
has no effect. Examples
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procedure Simplify(Expr : in out Expression) is null; -- see 3.9
-- By default, Simplify does nothing, but it may be overridden in extensions of ExpressionExtensions to Ada 95
6.a/2
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