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

[Gustaf Neumann]

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
>