[Laszlo-dev] Constructing objects from their string name

[P T Withington]

The correct fix is to fix getChildClass, which currently says:

         <method name="getChildClass">
             if (this.isleaf) return null;
             return this.constructor.classname;
         </method>

I guess the confusion is that it implies it returns a class, but it is  
actually returning a class _name_ (a string).

There are two choices of how to fix it.  If you need a tag name,  
because you are going to look it up in the `lz` module (as is done in  
say, baselist#addItem) you want:

   this.constructor.tagname

If you look this up in lz:

   lz[this.constructor.tagname]

you will get the constructor for the class that implements that tag.

But, if you just want the constructor directly, just say:

   this.constructor

It should always be the case that:

   lz[this.constructor.tagname] === this.constuctor

There's a bunch of confusion that has been introduced because we have  
made classnames non-global, and they don't necessarily match the name  
of the tag they implement.  (They never did for the LFC, we are now  
just uniform for all classes that implement tags).

I guess the confusion is increased because to the LZX programmer, when  
they say:

   <class name="foo" ...

they think they have created a class named `foo`, but really they have  
created a (Javascript) class with an anonymous name that implements  
the tag named `foo`.  The mapping from tag name to implementation  
class is through the `lz` table.  Perhaps we should rename the  
Javascript `classname` property to `implementationclassname` or  
perhaps get rid of it altogether, as it seems to only be a source of  
confusion...  I'll leave it to you if you want to file an improvement  
request to that effect.

---

In any case, please grep around the components in case `classname` is  
being mis-used elsewhere in the components.  Thanks!

On 2008-04-28, at 19:42 EDT, Philip Romanik wrote:

> Hi Tucker,
>
> There is a bug in the tree object caused by code in basetree.lzx:
>
>            var c = this.getChildClass();
>            if (c != null) {
>                new c(this, args, null, true);
>            }
>
> The dhtml error is TypeError: c is not a constructor.
>
> The code is trying to construct an object given the string name of  
> the class, ie:
>
> 	new lz.tree.classname
>
> Is the correct fix to do the equivalent of:
> 	new ConstructorMap[lz.tree.tagname]
>