Re: Renaming primitives.

["Jeffrey R.Carter" <spam.jrcarter.not@spam.acm.org.not>]

On 2024-01-10 11:37, Blady wrote:
> 
>     package Loggings is
>        type Logging is tagged record
>           Output : Ada.Text_IO.File_Access;
>        end record;
>        procedure Log (Handler : Logging; Msg : String);
>     end Loggings;
>     My_Handler : aliased Loggings.Logging := (Output => Ada.Text_IO.Current_Output);
>     My_Generic_Handler : access Loggings.Logging'Class := My_Handler'Access;
>     procedure My_Log_3 (Msg : String) renames My_Generic_Handler.Log;

My_Generic_Handler.Log is shorthand for My_Generic_Handler.all.Log. According to 
AARM 8.5.4(5.e/5) (http://www.ada-auth.org/standards/22aarm/html/AA-8-5-4.html), 
the renaming also renames the prefixing object and passes it to calls to the 
renamed subprogram: "The prefix in such a case is essentially renamed and passed 
to any calls of the renamed subprogram."

So if I understand this correctly the renaming is roughly equivalent to

<anonymous> : Loggings.Logging renames My_Generic_Handler.all;
procedure My_Log_3 (Handler : Loggings.Logging := <anonymous>; Msg : String) 
renames Loggings.Logging.Log;

except that My_Log_3 is called with only a String parameter even when using 
positional notation.

Another way to look at it is that

    My_Log_3 ("msg");

is implemented as

    <anonymous>.Log (Msg => "msg");

 > What is happening if My_Generic_Handler change?
 >
>        type Full_Logging is new Logging with null record;
>        procedure Log (Handler : Full_Logging; Msg : String);
> ...
>     My_Full_Handler : aliased Loggings.Full_Logging := (Output => 
> Ada.Text_IO.Current_Output);
> ...
>     My_Generic_Handler := My_Full_Handler'Access;
> 
> Well, logically (?), My_Log_3 follows the change and outputs with Full_Logging.

No, My_Log_3 continues to call Log with My_Handler as the object, IIUC.

> Unfortunately, GNAT claims renaming with several parameters.
> I add:
>        procedure Log (Handler : Logging; Msg : String; Err : Natural);
> ...
>     procedure My_Log_4 (Msg : String; Err : Natural) renames 
> My_Generic_Handler.Log;
> 
> I got:
> test_20240110_renproc.adb:47:14: error: too many arguments in call to "log"
> 
> Is it a correct or a GNAT issue?

I'm not sure what is going on here. This looks correct to me.

-- 
Jeff Carter
"Fundamental improvements in performance
are most often made by algorithm changes,
not by tuning."
Elements of Programming Style
201