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6.4 Subprogram Calls -- TOC

(1)
A subprogram call is either a procedure_call_statement or a function_call; it invokes the execution of the subprogram_body. The call specifies the association of the actual parameters, if any, with formal parameters of the subprogram.
Syntax
(2)
       procedure_call_statement ::=
           procedure_name;
         | procedure_prefix actual_parameter_part;
(3)
       function_call ::=
           function_name
         | function_prefix actual_parameter_part
(4)
       actual_parameter_part ::=
           (parameter_association {, parameter_association})
(5)
       parameter_association ::=
          [formal_parameter_selector_name =>] explicit_actual_parameter
(6)
       explicit_actual_parameter ::= expression | variable_name
(7)
Name Resolution Rules
(8)
The name or prefix given in a procedure_call_statement shall resolve to denote a callable entity that is a procedure, or an entry renamed as (viewed as) a procedure. The name or prefix given in a function_call shall resolve to denote a callable entity that is a function. When there is an actual_parameter_part, the prefix can be an implicit_dereference of an access-to-subprogram value.
(9)
A subprogram call shall contain at most one association for each formal parameter. Each formal parameter without an association shall have a default_expression (in the profile of the view denoted by the name or prefix). This rule is an overloading rule (see 8.6).
Dynamic Semantics
(10)
For the execution of a subprogram call, the name or prefix of the call is evaluated, and each parameter_association is evaluated (see 6.4.1). If a default_expression is used, an implicit parameter_association is assumed for this rule. These evaluations are done in an arbitrary order. The subprogram_body is then executed. Finally, if the subprogram completes normally, then after it is left, any necessary assigning back of formal to actual parameters occurs (see 6.4.1).
(11)
The exception Program_Error is raised at the point of a function_call if the function completes normally without executing a return_statement.
(12)
A function_call denotes a constant, as defined in 6.5; the nominal subtype of the constant is given by the result subtype of the function.
Examples
(13)
Examples of procedure calls:
(14)
       Traverse_Tree;                                               --  see 6.1
       Print_Header(128, Title, True);                              --  see 6.1
(15)
       Switch(From => X, To => Next);                               --  see 6.1
       Print_Header(128, Header => Title, Center => True);          --  see 6.1
       Print_Header(Header => Title, Center => True, Pages => 128); --  see 6.1
(16)
Examples of function calls:
(17)
       Dot_Product(U, V)   --  see 6.1 and 6.3
       Clock               --  see 9.6
       F.all               --  presuming F is of an access-to-subprogram type -- see 3.10
(18)
Examples of procedures with default expressions:
(19)
       procedure Activate(Process : in Process_Name;
                          After   : in Process_Name := No_Process;
                          Wait    : in Duration := 0.0;
                          Prior   : in Boolean := False);
(20)
       procedure Pair(Left, Right : in Person_Name := new Person);   --  see 3.10.1
(21)
Examples of their calls:
(22)
       Activate(X);
       Activate(X, After => Y);
       Activate(X, Wait => 60.0, Prior => True);
       Activate(X, Y, 10.0, False);
(23)
       Pair;
       Pair(Left => new Person, Right => new Person);

(24)
Examples
(25)
Examples of overloaded subprograms:
(26)
       procedure Put(X : in Integer);
       procedure Put(X : in String);
(27)
       procedure Set(Tint   : in Color);
       procedure Set(Signal : in Light);
(28)
Examples of their calls:
(29)
       Put(28);
       Put("no possible ambiguity here");
(30)
       Set(Tint   => Red);
       Set(Signal => Red);
       Set(Color'(Red));
(31)
       --  Set(Red) would be ambiguous since Red may
       --  denote a value either of type Color or of type Light

Subclauses

  1. Parameter Associations


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