6.3 Subprogram Bodies
1
[A subprogram_body specifies
the execution of a subprogram.]
Syntax
2/2
{
AI95-00218-03}
subprogram_body ::=
[overriding_indicator]
subprogram_specification is
declarative_part
begin
handled_sequence_of_statements
end [
designator];
3
If a designator
appears at the end of a subprogram_body, it
shall repeat the defining_designator of the
subprogram_specification.
Legality Rules
4
[In contrast to other bodies,] a
subprogram_body
need not be the completion of a previous declaration[, in which case
the body declares the subprogram]. If the body is a completion, it shall
be the completion of a
subprogram_declaration
or
generic_subprogram_declaration. The profile
of a
subprogram_body that completes a declaration
shall conform fully to that of the declaration.
{full
conformance (required)} Static Semantics
5
A subprogram_body is considered
a declaration. It can either complete a previous declaration, or itself
be the initial declaration of the subprogram.
Dynamic Semantics
6
{elaboration (non-generic
subprogram_body) [partial]} The elaboration
of a non-generic
subprogram_body has no other
effect than to establish that the subprogram can from then on be called
without failing the Elaboration_Check.
6.a
Ramification: See
12.2
for elaboration of a generic body. Note that protected
subprogram_bodies
never get elaborated; the elaboration of the containing
protected_body
allows them to be called without failing the Elaboration_Check.
7
{execution (subprogram_body)
[partial]} [The execution of a
subprogram_body
is invoked by a subprogram call.] For this execution the
declarative_part
is elaborated, and the
handled_sequence_of_statements
is then executed.
Examples
8
Example of procedure
body:
9
procedure Push(E : in Element_Type; S : in out Stack) is
begin
if S.Index = S.Size then
raise Stack_Overflow;
else
S.Index := S.Index + 1;
S.Space(S.Index) := E;
end if;
end Push;
10
Example of a function
body:
11
function Dot_Product(Left, Right : Vector) return Real is
Sum : Real := 0.0;
begin
Check(Left'First = Right'First and Left'Last = Right'Last);
for J in Left'Range loop
Sum := Sum + Left(J)*Right(J);
end loop;
return Sum;
end Dot_Product;
Extensions to Ada 83
11.a
{
extensions to Ada 83}
A
renaming_declaration may be used instead of
a
subprogram_body.
Wording Changes from Ada 83
11.b
The syntax rule for subprogram_body
now uses the syntactic category handled_sequence_of_statements.
11.c
The declarative_part
of a subprogram_body is now required; that
doesn't make any real difference, because a declarative_part
can be empty.
11.d
We have incorporated some rules from RM83-6.5
here.
11.e
RM83 forgot to restrict the definition of elaboration
of a subprogram_body to non-generics.
Wording Changes from Ada 95
11.f/2
{
AI95-00218-03}
Overriding_indicator
is added to subprogram_body.
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