Re: "subprogram must not be deeper than access type"

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 03/10/2020 06:39, andrew...@gmail.com wrote:
> Hello,
> 
> I'm trying my hand at a small rosettacode.org example:
> 
> https://codeshare.io/an080j
> 
> What I don't understand is when I'm creating the various packages to serve as handlers, I get the following compile-time errors:
> 
> gprbuild : event_handlers_window.adb:13:03: instantiation error at gtk-handlers.ads:1039
> event_handlers_window.adb:13:03: subprogram must not be deeper than access type
> event_handlers_window.adb:14:03: instantiation error at gtk-handlers.ads:437
> event_handlers_window.adb:14:03: subprogram must not be deeper than access type
> 
> How am I making a subprogram deeper than an access type exactly?

The access type to the handler function is declared at the library 
level. Your handler subprogram is declared inside the body of 
Event_Handlers_Window, which is one step deeper than the library level.

You can:

1. Move the handler function into a package. A library package would be 
on the same level with the access type declaration. That is the 
recommended way.

2. You can circumvent accessibility checks by declaring a local access 
type to the function in the procedure (which would be same level) and 
then convert from this type to the handler type using 
Unchecked_Conversion. This is not recommended, obviously.

3. Specifically for delete and destroy events in GtkAda Contributions 
the package Gtk.Missed defines ready-to-use handlers as in the solution #1.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de