Just did a few different tests. Since Element_Type is derived from tagged
type Base_Type, the On_Destroy procedure is inherited and there is an
implicit On_Destory(Object : in out Element_Type) created in
Gnoga.Gui.Elements. When you provide a "use" clause in your main
subprogram, it brings that inherited version into scope. Then you create
your On_Destroy(Object : in out Base_Type'Class) procedure. At this point
you have two On_Destroy procedures in scope. When you try to assign it to
the On_Destroy_Handler procedure, it can't tell which of the two versions
of On_Destroy you want to take the 'Access of.
I think the error messages could be clearer, but I think that is correct
operation as far as the compiler is concerned. I don't know if it can
resolve the 'Access based on the expected prototype. General user thought
process might expect that the compiler can pick the one that matches the
Action_Event prototype, but I am not a compiler writer, so I am not sure
how easy it is to do that nor do I know what the standard dictates for this.
On Sun, May 14, 2017 at 10:04 AM, Jeremiah Breeden <
jeremiah.bree...@gmail.com> wrote:
> The error seems off to me. What I found was it was your "use
> Gnoga.Gui.Element" line. In seems to expose the On_Destroy from
> Gnoga.Gui.Base into scope so that your On_Destroy method and the one in
> Gnoga.Gui.Base conflict somehow.
>
> Taking out the use and adding to Gnoga.Gui.Element. to the various calls
> is an alternate way of fixing it.
>
> I'm not sure why the two procedures conflict. They have different
> signatures, and the conflicting procedure isn't even in the package that is
> "use"ed
>
> This might be a question for comp.lang.ada. If I get time later, I'll try
> and parse through the RM to see if this is a bug or not, but it does seem
> odd. Maybe inherited functions of tagged types get exposed to the package
> that extends those types. If so, that is why On_Destroy would conflict in
> your call. Going only by the name of the procedure with not context, it
> happens to chose the one from Gnoga.Gui.Base, which doesn't match the
> Action_Event prototype.
>
> On Sun, May 14, 2017 at 4:33 AM, Pascal <blady-...@users.sf.net> wrote:
>
>> Hello,
>>
>> I've added a destroy handler to multiuser.adb test program:
>>
>>
>>
>> But I've got the following error with GNAT GPL 2016:
>>
>> gprbuild -ws -c -f -u -P/gnoga-code/test/test.gpr
>> -XLIB_COMPONENTS_BUILD=default -XPRJ_TARGET=OSX -XPRJ_BUILD=Debug
>> multiuser.adb
>> gcc -c -gnaty3abcefhiklM120nOprsStu -gnat2012 -gnatW8 -g -gnata -gnatq
>> -gnatQ -gnatw.eH.YD -gnatVa -gnato -fstack-check -gnatf -gnateE -gnateF
>> -gnatec=/gnoga-code/pragma_debug.adc -fno-common multiuser.adb
>> multiuser.adb:64:07: warning: "App" is not modified, could be declared
>> constant
>> multiuser.adb:81:07: warning: "App" is not modified, could be declared
>> constant
>> multiuser.adb:94:07: warning: "App" is not modified, could be declared
>> constant
>> multiuser.adb:103:07: warning: "App" is not modified, could be declared
>> constant
>> multiuser.adb:109:07: warning: variable "App" is not referenced
>> multiuser.adb:119:07: warning: "App" is not modified, could be declared
>> constant
>> multiuser.adb:193:43: no candidate interpretations match the actuals:
>> multiuser.adb:193:43: missing argument for parameter "Object" in call to
>> "On_Destroy" declared at line 115
>> multiuser.adb:193:43: missing argument for parameter "Object" in call to
>> "On_Destroy" (inherited) at gnoga-gui-element.ads:51
>> multiuser.adb:193:43: context requires function call, found procedure name
>> multiuser.adb:193:53: ==> in call to inherited operation
>> "On_Destroy_Handler" at gnoga-gui-window.ads:56
>> multiuser.adb:218:07: warning: "D" modified by call, but value never
>> referenced
>> gprbuild: *** compilation phase failed
>> [2017-05-14 10:21:43] process exited with status 4, elapsed time: 00.69s
>>
>> If I change ligne 193 to:
>>
>> App.Main_Window.On_Destroy_Handler (Multiuser.On_Destroy'Unrestri
>> cted_Access);
>>
>> No more errors.
>>
>> Why these errors not so much clear are issued?
>> Why local procedure On_Destroy isn't visible?
>>
>> Thanks, Pascal.
>> http://blady.pagesperso-orange.fr
>>
>>
>>
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>
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