6.1 Subprogram Declarations
1
Syntax
2/3
3/2
4/2
4.1/2
4.2/2
5
6
7
8
9
10/2
{
AI95-00395-01}
The sequence of characters in an
operator_symbol
shall form a reserved word, a delimiter, or compound delimiter that corresponds
to an operator belonging to one of the six categories of operators defined
in clause
4.5.
10.a/3
Reason: {
AI95-00395-01}
{
AI05-0090-1}
The “sequence of characters” of the string literal of the
operator is a technical term (see
2.6), and
does not include the surrounding quote characters. As defined in
2.2,
lexical elements are “formed” from a sequence of characters.
Spaces are not allowed, and upper and lower case is not significant.
11
12
13/2
14
15/3
16
mode ::= [
in] |
in out |
out
Name Resolution Rules
17
A
formal parameter is
an object [directly visible within a
subprogram_body]
that represents the actual parameter passed to the subprogram in a call;
it is declared by a
parameter_specification.
For a formal parameter, the expected type for its
default_expression,
if any, is that of the formal parameter.
Legality Rules
18/3
{
AI05-0143-1}
The
parameter mode of a formal parameter conveys
the direction of information transfer with the actual parameter:
in,
in out, or
out. Mode
in is the default, and is the
mode of a parameter defined by an
access_definition.
18.a/3
19
20/3
20.a/3
Ramification: {
AI95-00348-01}
{
AI05-0177-1}
Abstract subprograms , null procedures, and expression functions are
not declared by
subprogram_declarations,
and so do not require completion (although the latter two can
be
completions). Protected subprograms are declared by
subprogram_declarations,
and so require completion. Note that an abstract subprogram is a subprogram,
a null procedure is a subprogram, an expression function is a subprogram,
and a protected subprogram is a subprogram, but a generic subprogram
is not a subprogram.
20.b/3
Proof: {
AI05-0229-1}
When the Import aspect is True for any entity, no completion is allowed
(see
B.1).
21
21.a
Static Semantics
22
The
profile of (a view
of) a callable entity is either a
parameter_profile
or
parameter_and_result_profile[;
it embodies information about the interface to that entity — for
example, the profile includes information about parameters passed to
the callable entity. All callable entities have a profile — enumeration
literals, other subprograms, and entries. An access-to-subprogram type
has a designated profile.] Associated with a profile is a calling convention.
A
subprogram_declaration
declares a procedure or a function, as indicated by the initial reserved
word, with name and profile as given by its specification.
23/2
23.1/3
24/2
{
AI95-00231-01}
{
AI95-00254-01}
{
AI95-00318-02}
An
access parameter is a formal
in
parameter specified by an
access_definition.
An
access result type is a function result
type specified by an
access_definition.
An access parameter or result type is of an anonymous access type (see
3.10). [Access parameters of an access-to-object
type allow dispatching calls to be controlled by access values. Access
parameters of an access-to-subprogram type permit calls to subprograms
passed as parameters irrespective of their accessibility level.]
24.a/2
Discussion: {
AI95-00318-02}
Access result types have normal accessibility and thus don't have any
special properties worth noting here.
25
The
subtypes of a profile are:
26
For any non-access parameters, the nominal subtype
of the parameter.
27/2
{
AI95-00254-01}
For any access parameters of an access-to-object type, the designated
subtype of the parameter type.
27.1/3
{
AI95-00254-01}
{
AI05-0164-1}
For any access parameters of an access-to-subprogram type, the subtypes
of the designated profile of the parameter type.
28/2
28.1/2
{
AI95-00318-02}
For any access result type of an access-to-object type, the designated
subtype of the result type.
28.2/3
{
AI95-00318-02}
{
AI05-0164-1}
For any access result type of an access-to-subprogram type, the subtypes
of the designated profile of the result type.
29
[
The
types of a profile
are the types of those subtypes.]
30/3
30.1/2
Dynamic Semantics
31/2
32
33
34
3 The evaluation of
default_expressions
is caused by certain calls, as described in
6.4.1.
They are not evaluated during the elaboration of the subprogram declaration.
35
4 Subprograms can be called recursively
and can be called concurrently from multiple tasks.
Examples
36
Examples of subprogram
declarations:
37
procedure Traverse_Tree;
procedure Increment(X :
in out Integer);
procedure Right_Indent(Margin :
out Line_Size); --
see 3.5.4
procedure Switch(From, To :
in out Link); --
see 3.10.1
38
function Random
return Probability; --
see 3.5.7
39
function Min_Cell(X : Link)
return Cell; --
see 3.10.1
function Next_Frame(K : Positive)
return Frame; --
see 3.10
function Dot_Product(Left, Right : Vector)
return Real; --
see 3.6
40
function "*"(Left, Right : Matrix)
return Matrix; --
see 3.6
41
Examples of in
parameters with default expressions:
42
procedure Print_Header(Pages :
in Natural;
Header :
in Line := (1 .. Line'Last => ' '); --
see 3.6
Center :
in Boolean := True);
Extensions to Ada 83
42.a
42.b
Program units that are library units may have
a
parent_unit_name
to indicate the parent of a child (see Section 10).
Wording Changes from Ada 83
42.c
We have incorporated the rules from RM83-6.5,
“Function Subprograms” here and in
6.3,
“
Subprogram Bodies”
42.d
We have incorporated the definitions of RM83-6.6,
“Parameter and Result Type Profile - Overloading of Subprograms”
here.
42.e
Extensions to Ada 95
42.f/2
42.g/2
42.h/2
{
AI95-00318-02}
The return type of a function can be an anonymous access type.
Wording Changes from Ada 95
42.i/2
{
AI95-00254-01}
A description of the purpose of anonymous access-to-subprogram parameters
and the definition of the profile of subprograms containing them was
added.
42.j/2
42.k/2
42.l/2
Extensions to Ada 2005
42.m/3
{
AI05-0142-4}
Parameters can now be explicitly aliased, allowing
parts of function results to designate parameters and forcing by-reference
parameter passing.
42.n/3
{
AI05-0143-1}
The parameters of a function can now have any mode.
42.o/3
Wording Changes from Ada 2005
42.p/3
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe