Re: [Xotcl] [NX] Passing arguments to an object's constructor

From: Gustaf Neumann <neumann_at_wu-wien.ac.at>
Date: Tue, 29 Nov 2011 09:21:10 +0100

Dear Arthur,

The short answer is: object parameter are the preferred way,
these fit better to dynamic languages and avoid several
potential anomalies (see e.g. the example from the slides of
the 2011 Tcl conference)

The longer answer (not necessarily introductory): For NX the
object parameters are the only way, but the object
parameters can be positional and/or non-positional, as for
parameter definitions for methods. The object signature is
derived from the slots of the class hierarchy from which an
object is instantiated. The derived signature is a sequence
of positional and non-positional parameter specs. For object
parameters, typically most parameter specs are
non-positional, just the last spec is positional (the init
script). Certainly, this can be extended:

Here is a short example.

    nx::Class create C { :property x }
    nx::Class create D -superclass C { :property y }
    D create d1 -y 123

This script implies an object signature for D of the form
"-x -y .... {init-script}" (simplified).
If one adds a positional parameter

    nx::Class create E -superclass D { :property {z ""} {set :positional 1} }

the signature of E becomes "z -x -y ... {init-script}" (also
simplified).
With this signature, one can create objects e.g. via

    E create e1 "hello world"

For the positional parameters, a position can be added (the
non-pos paramters start at position 1, so use e.g. 0.1, 0.2
etc.). However, for beginners i would recommend to stick to
the default behavior with just non-positional object
parameters...

best regards
Gustaf Neumann

PS: XOTcl (and XOTcl 2) support method parameters for
constructors, and since XOTcl 2 and NX are based on nsf,
this could be done as well in NX (somewhat contradictory to
above, but such a modification would require low-level
modifications to NX, it would not be the same NX). However,
when method parameters to constructors should be as well
positional and non-positional, these tend to become a source
for confusion, at least, if one wants to support derived
object-parameters....

On 28.11.11 21:53, Arthur Schreiber wrote:
> Hello everyone,
>
> Is there any way to pass arguments to the init method in NX (as in XOTcl)?
> Or is using object parameters on initialization the preferred way in NX
> to initialize an objects instance variables?
>
> Thanks,
> Arthur
>