[Laszlo-dev] Proposal to tweak the behavior of attributes with a setter and an initial value

[André Bargull]

>
> Pro:
>
> The setter code for cases like the above will not be erroneously  
> skipped if the initial value is `null`.
>   

I'm not really sure many users actually use identity comparison, I 
assume they mostly use equality comparison. And if that assumption is 
correct, it won't make any difference to use `null` instead of `undefined`.

> Con:
>
> The setter code must take care checking the value of the attribute.   
> Since it will initially be `undefined`, referencing it as `this.foo`  
> will generate a warning in the swf8 runtime.  To avoid the warning,  
> the code must be re-written as `this['foo']`.
>   

That'll be for sure annoying for many people. But it's not only the
> reference to undefined property 'foo'
warning which will appear if the initial value is changed to 
`undefined`. Due to "implicit this" support and because it's impossible 
to differentiate between a property which is set to `undefined` and an 
`undefined` property in the swf8 runtime, also a debug-error will be 
generated:
> reference to undefined variable 'foo'
A simple testcase:
<canvas debug="true">
  <node>
    <attribute name="foo" />
    <handler name="oninit">
      this.foo = void 0;
      Debug.write(this.foo); // debug-warning: reference to undefined 
property 'foo'
      Debug.write(foo); // "implicit this" => debug-error: reference to 
undefined variable 'foo'
    </handler>
  </node>
</canvas>