Re: X11Ada - Is Unchecked_Conversion commonly required?

[jsa@alexandria.organon.com (Jon S Anthony)]

In article <33CAE473.4079@earthlink.net> James Thomas <jaimiethomas@earthlink.net> writes:

> What I've noticed is an apparent requirement to use Unchecked_Conversion
> an *awful* lot. Examples (I'll try to keep these succinct)follow. What I
> need to know is this - Am I just missing something here - or is this
> prevalent use of UC really needed with the Intermetrics bindings?

Unknown - you don't give enough information.  However, I can say this:
In my use of these bindings, I have not needed to use UC except for
the typical use in a callback structure (where X/Motif does not give
enough information to be able to do anything otherwise - in C/C++
these typically have a cast to the correct type).


> 1. When calling XtOpenDisplay, and passing X.Args.Argc to the argc
> parameter, it is necessary (?) to use UC to convert the type of the

No, pass the 'Access of this argument:

       Argc              => X.Args.Argc'Access,


> 2. More commonly - it is not uncommon to pass a widget to XtAddCallback
> as the "closure" parameter.  This was done rather simply when using 
> Telesoft's bindings, w/o using UC.

This is an example of callback "data", so UC will be needed.  I'm sure
UC was used in this context too - just under the covers.  Note that
the Intermetric bindings are "thin" (a Good Thing, IMO).


> 3. When using old-style args (not Va args), which is still required
> for some subprograms, it is necessary to use UC to stuff data into
> the XtArg.  UC was not needed in Telesoft's bindings.

Haven't done this, but that is probably true.


> I am finding more examples every day.  I am new to Ada 95 (but I'm an

The rule of thumb would be, anywhere the X/Motif docs (say the O'Reily
books) say to cast, you will probably need to UC, as these are thin
bindings and directly reflect the C level semantics.  As I say, I
think this is a good thing as it doesn't pretend that the underlying
SW is anything but your typical C rubbish.  Plus, you can use the C
references pretty much verbatim - no need for extraneous documentation
for how the thick bindings work.

/Jon
-- 
Jon Anthony
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