AW: [Xotcl] destroy invoked by object move?

[Gustaf Neumann]

mail at xdobry.de schrieb:
> Hi Scott!
>
> Indeed move in XOTcl is copy+destroy and it is implemented in XOTcl itself.
>
> ...
> After I have discovered, what indeed move is, I have changed the implementation.
> I think it is a little trap in XOTcl, because many user thinks it is magic fast and do not really destory objects. Indeed it is quite expensive.
>   
note, that there is no "namespace rename" command in tcl as well. Since
xotcl uses tcl namespaces, in the general case a rename command requires
to handle all references (and pointers in C) to namesspaces (including 
traces,
tcl-command names, aliases, namespace imports, nested namespaces, ...),
when a namespace (with all its children) is renamed.
Therefore in general, a "namespace rename" is much more expensive than
a "command rename". note, that tcl has no "variable rename" command
as well.  So, adding such a functionality would require some amount
of C hacking and quite a strong coupleing with the tcl internals.

The implementation of move as copy+destroy is a compromise between
simplicity and functionality. I can imagine cases, where one wants
to have more or less the equivalent to a copy constructor when
copy occurs and maybe something different when a move happens.
However, since all methods are equal in xotcl, it is quite simple
for a poweruser of xotcl to overload copy/move and add applicaton
specific addtional behavior to it. if one does not like the side-effects
of destroy in a move, a custom move operation can set in instance
variable "__during_move__" and query this from the destroy
method to change its behavior.

hope, this helps...

-gustaf neumann

> Artur
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