Re: Calling through function pointer--syntax question

[Tucker Taft <stt@averstar.com>]

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Adam Beneschan wrote:
> ...
> At the risk of being taunted a second time, and possibly even having a
> cow hurled down on top of me (or perhaps some other unit of
> livestock), I feel that I need to respond again. 

Despite my earlier response, I now agree with you.
I hadn't looked at your example closely enough the
first time.


> ...
> Anyway, it seems to me that the procedure call in question *is*
> ambiguous, contrary to what everyone else (including someone's
> compiler) says, and I'll try to explain in more precise detail why I
> think so:
> 
> The relevant declarations are:
> 
>     type func_ptr is access function (param : integer) return integer;
>     function func (y : integer := 4) return func_ptr;
>     procedure P (x : in integer);
>     procedure P (x : in func_ptr);
> 
> and my question is about the procedure call:
> 
>     P (func (5));
> 
> Obviously, one acceptable interpretation is that "func" is called with
> the parameter 5, returning a func_ptr, and this func_ptr is passed to
> the second P.
> 
> I believe the other interpretation is also acceptable, however: "func"
> is called with a default parameter, 4.  This returns a function
> pointer.  This function pointer is dereferenced, and the designated
> function is called with the parameter 5.  This returns an integer, and
> the resulting integer is passed to the first P.

Yes, I agree with your analysis.

> ... Is there an error in my
> line of thought?

No.
(And my favorite Ada front end agrees with you too -- I should
have checked with it first!)

[I have attached a listing.]

> 
>                                 -- thanks, Adam

-- 
-Tucker Taft   stt@avercom.net   http://www.avercom.net
Chief Technology Officer, AverCom Corporation (A Titan Company) 
Burlington, MA  USA (AverCom was formerly the Commercial Division of AverStar:
http://www.averstar.com/~stt)

[-- Attachment #2: test_ambig.ada.lst --]
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Source file: test_ambig.ada   Mon Jun 11 13:30:34 2001

    1 procedure test_ambig is
    2     type func_ptr is access function (param : integer) return integer;
    3     function func (y : integer := 4) return func_ptr is begin return null; end;
    4     procedure P (x : in integer) is begin null; end;
    5     procedure P (x : in func_ptr) is begin null; end;
    6 
    7 -- and my question is about the procedure call:
    8 
    9 begin
   10 
   11     P (func (5));       
          *
*****Error: LRM:8.6(31) Ambiguous call, possible definitions of P appear at
*****        line 5 of file test_ambig.ada, line 4 (same file).
   12 
   13 end;
   14 
   15