Re: [Xotcl] forwarding

Dear Victor,

The best approach for forwarding to a child object is either an alias, or a direct invocation of a subobject through the method interface. Consider the following code, where we have an object "obj" and an embedded child object "obj::child".

nx::Object create obj {

nx::Object create [self]::child { :public method foo {} {return [self]} }

:public alias a [self]::child :public forward f [self]::child }

One could certainly use as well a forward, but this is necessary. Technically, objects are Tcl commands, and Tcl commands and procs reside in a namespace. Therefore, by creating a child object of obj, one has to create in its namespace a cmd "child", which is in turn very similar to a per-object method. Therefore, one cannot define a per-object method "foo" and a child object "foo" at the same time.

The idiom to use an object as a container for subobject and delegate to these is quite common in some systems (used intensively in xotclIDE). In our previous releases of nx, the semantics of calling of the subobject have changed relative to XOTcl 1.6 due to the requirements of ensemble objects. The recent changes reintroduced backwards compatibility in this respect as well, leading to a probably more expected behavior in the case above (concerning "self" in the methods of the subobject). As you can see below the invocation of the child is the fastest approach.

? {obj a foo} {::obj::child} ? {obj f foo} {::obj::child} ? {obj child foo} {::obj::child}

v/child-obj-delegation.001: 0.71 mms, obj a foo (overhead 0.62) v/child-obj-delegation.002: 0.75 mms, obj f foo (overhead 0.65) v/child-obj-delegation.003: 0.65 mms, obj child foo (overhead 0.68)

Note, that this requires the head version of nx (which works now as well with Tcl version from fossil head); we will tag a new beta release soon, documentation updates are pending.

In case, one does not want to allow calls of the subobject via the method interface (3rd case above), one can use access control ("private" or "protected"). Maybe we add for nx some more syntactic sugar by allowing something along the lines of

nx::Object create obj {

:public child nx::Object bar { :public method foo {} {return [self]} }

:public alias a [self]::child :public forward f [self]::child }

for creating a child object "obj::bar" with public access.

-gustaf neumann

On 11.01.12 04:06, Victor Mayevski wrote:

Is it possible to do a forward in the following manner:

  obj public forward link %self::child-obj

The best I could do was:

  obj public forward link :child-obj

which I have to call in the following way: [obj link] mymethod

Also, I don't even know why it works that way, because I think it should work this way: obj public forward link -objframe :child-obj but that does not work.

Thanks _______________________________________________ Xotcl mailing list Xotcl@alice.wu-wien.ac.at http://alice.wu-wien.ac.at/mailman/listinfo/xotcl