Re: making a son benefit access ton an instanciation of a generic package required as a formal parameter to his father and instanciated by him

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

On 2018-01-21 21:15, Mehdi Saada wrote:
> Thanks Dmitry. I just stumpled against another exemple of your point 1, RM's paragraph 11.2.8:
> An exception_name of a choice shall not denote an exception declared in a generic formal package.
> 
> What ? Doesn't it make them almost useless, then ?!

Consider the same exception visible under different names coming from 
the same package. The compiler could not decide that when compiling the 
exception handler. But you can use an exception from a generic instance 
still.

It is a general problem with generics that something legal when 
compiling it might turn legal or illegal depending on actual formal 
parameters. In some cases Ada just ignores that, e.g. by treating things 
wrongly or in an unexpected way, in other cases it tries to prevent 
that. It is an uphill battle. There is no way to fix 
generics/templates/macros.

> It doesn't accept things like P1_instance.exception_name either,
> which I don't get at all. It
> should, if that rule ever was a concern about names hiding and such,
> your point 1 that is. How do I do to STILL use exceptions declared in
> generic package, in a handler ? I won't rewrite the package just for
> this. Each time I try, there's always more work than expected.

The rule is too keep it as simple as possible. If there is any way to 
ditch generics, do it. Use interfaces and tagged types, mix-ins, 
class-wide access discriminants etc to achieve polymorphism.

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