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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Formal Subprogram Access
Date: Fri, 9 Feb 2018 23:11:57 +0100
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Date: 2018-02-09T23:11:57+01:00
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Suppose I have something like

procedure Fpa_Proc (P : not null access procedure) is
    -- Empty
begin -- Fpa_Proc
    null;
end Fpa_Proc;

generic -- Fpa_Gen
    with procedure P;
procedure Fpa_Gen;

with Fpa_Proc;

procedure Fpa_Gen is
    -- Empty
begin -- Fpa_Gen
    Fpa_Proc (P => P'Access);
end Fpa_Gen;

(FPA for Formal Procedure Access)

FSF GNAT 7.2.0 rejects Fpa_Gen with the error

fpa_gen.adb:6:19: not subtype conformant with declaration at fpa_proc.adb:1
fpa_gen.adb:6:19: formal subprograms not allowed

which I think is correct. I can change it to have a wrapper procedure:

with Fpa_Proc;

procedure Fpa_Gen is
    procedure New_P is
       -- Empty
    begin -- New_P
       P;
    end New_P;
begin -- Fpa_Gen
    Fpa_Proc (P => New_P'Access);
end Fpa_Gen;

which compiles fine. But to my surprise, I can also rename P:

with Fpa_Proc;

procedure Fpa_Gen is
    procedure New_P renames P;
begin -- Fpa_Gen
    Fpa_Proc (P => New_P'Access);
end Fpa_Gen;

and this also compiles. I would think that if you can't take 'Access of a 
generic formal subprogram, then you shouldn't be able to take 'Access of a 
renaming of a generic formal subprogram. So I'm wondering if this last form is 
legal.

-- 
Jeff Carter
"Gentlemen, you can't fight in here. This is the War Room!"
Dr. Strangelove
30