Re: Access type to member procedure of instance (Object Oriented programming in Ada)

[ake.ragnar.dahlgren@gmail.com]

On Monday, November 19, 2012 10:59:42 AM UTC+1, ake.ragna...@gmail.com wrote:
> Not sure if this has already been discussed but: Is it possible to define a pointer to a member procedure of an instance? This problem has it's origin in the implementation of the MVC pattern for a GtkAda application. Consider the following: package Some_Package is type Message_Type is tagged null record; procedure Print(Message : Message_Type); end Some_Package; package body Some_Package is procedure Print (Message : Message_Type) is begin null; end Print; end Some_Package; Then it is possible to create the following Main application that compiles just fine: with Some_Package; procedure Main is Message : Some_Package.Message_Type; begin Message.Print; end Main; Is it possible to create a parameterless access type to the Message.Print procedure? The following application refuses to compile: with Some_Package; procedure Main is Message : Some_Package.Message_Type; Method_Ref : access procedure := Message.Print'Access; begin Method_Ref; end Main; The error message is: no selector "Print" for type "Message_Type" defined at some_package.ads:3 It is possible to create a workaround: with Some_Package; procedure Main is Message : Some_Package.Message_Type; procedure Method_Ref is begin Message.Print; end Method_Ref; begin Method_Ref; end Main; Is there a better way? Or is this the optimal way? Regards, Åke Ragnar Dahlgren

I want to thank everybody for replying. I had no idea about the "renames" feature as Randy pointed out. Brian expressed it very well: I am astonished!

As for the Gtkada application I have given up on implementing the MVC pattern using tagged types. Instead I choose the same approach as was done in the Ada in Denmark wiki.

Best regards,
Åke Ragnar Dahlgren