[Oberon] Oberon for a C++ user.

[Aubrey.McIntosh at alumni.utexas.net]

This snipped compiles under Component Pascal 1.7-rc1, and traps with a nil
procedure call.

MODULE TempProcvar;
TYPE
ParamProc = PROCEDURE ( p: INTEGER );
VAR
trouble* : ParamProc;
PROCEDURE UseProc ( method: ParamProc );
BEGIN
method( 42 )
END UseProc;
PROCEDURE Doit*;
BEGIN
UseProc (  trouble )
END Doit;
END TempProcvar.



On Fri, Sep 30, 2016 at 6:11 PM, Chris Burrows <chris at cfbsoftware.com>
wrote:

> > -----Original Message-----
> > From: Oberon [mailto:oberon-bounces at lists.inf.ethz.ch] On Behalf Of
> > Stéphane Aulery
> > Sent: Friday, 30 September 2016 6:19 AM
> > To: ETH Oberon and related systems
> > Subject: Re: [Oberon] Oberon for a C++ user.
> >
> > >
> > > I wonder if there is a way out.  Can this problem be solved within
> > the Oberon-1 framework?
> >
> > What you say is surprising. There are probably a good reason to
> > dismiss this problem. Anybody kwnow why please?
> >
>
> I'd like to see actual example code that illustrates the problem as I am
> not
> convinced it is a problem - at least not with the latest version of Oberon.
> As Srivas pointed out, e.g. in Project Oberon, if you want to assign an
> external procedure to a procedure variable, or you want to reference an
> external procedure variable you have to import the module that contains
> that
> procedure / procedure variable. If you have imported that module you can't
> unload it until the importing module is unloaded first.
>
> Oberon-2 does have additional object-oriented features. Maybe they cause an
> issue when mixed with the use of procedure variables? Procedure Varaiables
> might have been left in the language in the transition from original Oberon
> to Oberon-2 simply to avoid breaking backward-compatibility. It is likely
> there is no *need* to use procedure variables if you have these additional
> features. This is supported by the following quote from Hanspeter
> Mossenbock's book 'Object-Oriented Programming in Oberon-2':
>
> "Dynamic binding has also been known for a long time in the form of
> procedure variables. The activation of a procedure variable causes the
> invocation of the procedure contained in it at run time. Working with
> procedure variables, however, is troublesome and error-prone, while dynamic
> binding in object-oriented languages represents an elegant and reliable
> solution."
>
> It is also significant to note that Procedure Variables are documented as
> 'deprecated' in the .NET version of Component Pascal (the Oberon-2
> superset).
>
> Regards,
> Chris
>
> Chris Burrows
> CFB Software
> http://www.astrobe.com
>
>
> --
> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
> https://lists.inf.ethz.ch/mailman/listinfo/oberon
>



-- 
(email is my preferred communication media)
Aubrey McIntosh, Ph.D.
1502 Devon Circle
Austin TX 78723-1814
(512)-348-7401
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