10.1.3 Subunits of Compilation Units
1
Subunits are like child units, with these (important)
differences: subunits support the separate compilation of bodies only
(not declarations); the parent contains a body_stub
to indicate the existence and place of each of its subunits; declarations
appearing in the parent's body can be visible within the subunits.
Syntax
2
body_stub ::= subprogram_body_stub |
package_body_stub |
task_body_stub |
protected_body_stub
3/2
subprogram_body_stub ::=
[
overriding_indicator]
subprogram_specification is separate;
4
package_body_stub ::= package body defining_identifier is separate;
5
task_body_stub ::= task body defining_identifier is separate;
6
protected_body_stub ::= protected body defining_identifier is separate;
7
subunit ::= separate (
parent_unit_name)
proper_body
Legality Rules
8/2
The
parent body of a subunit
is the body of the program unit denoted by its
parent_unit_name.
The term
subunit is used to refer to a
subunit
and also to the
proper_body of a
subunit.
The
subunits of a program unit include any subunit that names
that program unit as its parent, as well as any subunit that names such
a subunit as its parent (recursively).
9
The parent body of a subunit shall be present in
the current environment, and shall contain a corresponding body_stub
with the same defining_identifier as the subunit.
10
A package_body_stub shall
be the completion of a package_declaration
or generic_package_declaration; a task_body_stub
shall be the completion of a task_declaration;
a protected_body_stub shall be the completion
of a protected_declaration.
11
In contrast, a
subprogram_body_stub
need not be the completion of a previous declaration, in which case the
_stub declares the subprogram. If the
_stub
is a completion, it shall be the completion of a
subprogram_declaration
or
generic_subprogram_declaration. The profile
of a
subprogram_body_stub that completes a
declaration shall conform fully to that of the declaration.
12
A subunit that corresponds to a
body_stub
shall be of the same kind (
package_,
subprogram_,
task_, or
protected_)
as the
body_stub. The profile of a
subprogram_body
subunit shall be fully conformant to that of the corresponding
body_stub.
13
A body_stub shall appear
immediately within the declarative_part of
a compilation unit body. This rule does not apply within an instance
of a generic unit.
14
The defining_identifiers
of all body_stubs that appear immediately
within a particular declarative_part shall
be distinct.
Post-Compilation Rules
15
For each body_stub, there
shall be a subunit containing the corresponding proper_body.
16
17
- Visibility within a subunit is
the visibility that would be obtained at the place of the corresponding
body_stub (within the parent body) if the
context_clause of the subunit were appended
to that of the parent body.
18
- The effect of the elaboration
of a body_stub is to elaborate the subunit.
Examples
19
The package Parent
is first written without subunits:
20
package Parent is
procedure Inner;
end Parent;
21
with Ada.Text_IO;
package body Parent is
Variable : String := "Hello, there.";
procedure Inner is
begin
Ada.Text_IO.Put_Line(Variable);
end Inner;
end Parent;
22
The body of procedure
Inner may be turned into a subunit by rewriting the package body as follows
(with the declaration of Parent remaining the same):
23
package body Parent is
Variable : String := "Hello, there.";
procedure Inner is separate;
end Parent;
24
with Ada.Text_IO;
separate(Parent)
procedure Inner is
begin
Ada.Text_IO.Put_Line(Variable);
end Inner;
Sponsored by Ada-Europe