Ada Reference Manual (Ada 2022) — Legal Information

6.5.1 Nonreturning Subprograms

Specifying aspect No_Return to have the value True indicates that a subprogram cannot return normally; it may, for example, propagate an exception or loop forever.

Paragraphs 2 and 3 were moved to Annex J, “Obsolescent Features”.

Static Semantics

3.1/5

For a subprogram or generic subprogram, the following language-defined representation aspect may be specified:

3.2/3

No_Return

The type of aspect No_Return is Boolean. When aspect No_Return is True for an entity, the entity is said to be nonreturning.

3.3/5

If directly specified, the aspect_definition shall be a static expression. When not directly specified, if the subprogram is a primitive subprogram inherited by a derived type, then the aspect is True if any corresponding subprogram of the parent or progenitor types is nonreturning. Otherwise, the aspect is False.

3.4/5

If a generic subprogram is nonreturning, then so are its instances. If a subprogram declared within a generic unit is nonreturning, then so are the corresponding copies of that subprogram in instances.

Legality Rules

4/3

Aspect No_Return shall not be specified for a null procedure nor an instance of a generic unit.

5/2

A return statement shall not apply to a nonreturning procedure or generic procedure.

5.1/5

Any return statement that applies to a nonreturning function or generic function shall be a simple_return_statement with an expression that is a raise_expression, a call on a nonreturning function, or a parenthesized expression of one of these.

6/5

A subprogram shall be nonreturning if it overrides a dispatching nonreturning subprogram. In addition to the places where Legality Rules normally apply (see 12.3), this rule applies also in the private part of an instance of a generic unit.

7/5

If a renaming-as-body completes a nonreturning subprogram declaration, then the renamed subprogram shall be nonreturning.

Paragraph 8 was deleted.

Dynamic Semantics

9/2

If the body of a nonreturning procedure completes normally, Program_Error is raised at the point of the call.

Examples

10/5

Example of a specification of a No_Return aspect:

11/3

procedure Fail(Msg : String)  -- raises Fatal_Error exception
   with No_Return;
   -- Inform compiler and reader that procedure never returns normally

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