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From: Stephen Leake <stephen_leake@stephe-leake.org>
Newsgroups: comp.lang.ada
Subject: anonymous aggregates?
Date: Fri, 31 Aug 2012 06:22:35 -0400
Message-ID: <85mx1bwec4.fsf@stephe-leake.org>
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Date: 2012-08-31T06:22:35-04:00
List-Id: <comp.lang.ada>

Occasionally I have the following pattern:

declare
    A : Integer;
    B : Float;

    procedure Foo (A : out Integer; B : out Float);
begin
   Foo (A, B);
   ...
end;

where Foo initializes A, B.

In general, I prefer to initialize variables in the declaration, and
declare them constant if possible. But I can't do that here.

One option in current Ada is to declare a record type;

declare
    type Foo_Return_Type is record
        A : Integer;
        B : Float;
    end record;

    function Foo return Foo_Return_Type is
    begin
        return
            (A => 1,    
             B => 2.0);
    end Foo;

    A_B : constant Foo_Return_Type := Foo;
begin
   ...
end;

But that seems like overkill, especially since the code in "..." must be
edited; all references to A must be replaced by A_B.A.

If we introduce the notion of "anonymous aggregates" (styled after
"anonymous arrays"), we could do this:

declare
    function Foo return
     (A : Integer;
      B : Float) 
    is begin
        return
            (A => 1,    
             B => 2.0);
    end Foo;

    (A : constant integer,
     B : constant Float) := Foo;
begin
   ...
end;

I haven't thought much about how this would be implemented.

-- 
-- Stephe