[Xotcl] Re: [Xotcl] Object mixin with passing init args ?

[uwe.zdun@uni-essen.de]

>>>>> "ZV" == Zoran Vasiljevic <zoran@munich.com> writes:

ZV> Hi XOTcl gurus!
ZV> Consider this:

ZV> % Class Foo
ZV> % Foo instproc init {dir} {puts hallo}

ZV> % Class Bar
ZV> % Bar bar
ZV> % bar mixin Foo
ZV> no value given for parameter "dir" to "init"

ZV> After snooping arround I've found out that mixin's does
ZV> not allow any argument passing to the mixin class initializer.

ZV> Is this something normal ? If one needs such functionality
ZV> are there any workarounds ?

1. That's a general problem of composing classes with the
next-path. "mixin" calls the constructor. If different constructors
are composed & constructors should receive args, nearly always they
should not receive the same args ...

Therefore, with "generic" methods, like constructors, filters, etc.,
it is almost always a good choice to use "args" as argument, like:

% Class Foo
Foo
% Foo instproc init args {puts hallo}
% Class Bar
Bar
% Bar bar
bar
% bar mixin Foo
hallo
%

we've once discussed to enforce this (with filters its a MUCH bigger
problem, because they nearly always receive different args), but for
the sake of compatibility with OTcl its still in the responsibility of
the programmer.

2. However, in the "mixin" case we could enable argument passing,
because "mixin" has just one argument? The rest could be passed to
"init". any objections?

--Uwe

-- 
Uwe Zdun
Specification of Software Systems, University of Essen
Phone: +49 201 81 00 332, Fax: +49 201 81 00 398
zdun@xotcl.org, uwe.zdun@uni-essen.de