Re: [Dynapi-Dev] An easy way to Subclass/Overwrite functions

[Benoit M. <mar...@ma...>]

See my comments bellow

On Friday, April 4, 2003, at 02:25  PM, Raymond Irving wrote:

>
> Please see below:
>
> --- Benoit Marchant <mar...@ma...> wrote:
>> I would prefer
>> I  prefer the syntax super.setSize(w,h).
>>
>> What about adding
>>
>> DynAPIObject.prototype.overwrite = function(sC,n) {
>>      var c = this.frame[sC];
>>      var superMethod =
>> c.prototype._superPrototype[n];
>>      var capitalized = n.charAt(0).toUpperCase() +
>> n.substring(1,n.length);
>>      var	superMethodOverridename = 'super'+
>> capitalized;
>>      if(superMethod &&
>> !c.prototype[superMethodOverridename]) {
>>          c.prototype[superMethodOverridename] =
>> superMethod;
>>      }
>> };
>>
>> and in the class you want to overwrite:
>> p.setSize = function(width,height) {
>> 	this.superSetSize (widt h,height);
>> 	//Then do your stuff
>> }
>> dynapi.overwrite('EventObject','setSize');//which
>> basically does
>> p.superSetSize = mySuperClass.prototype.setSize
>>
>>
>> that way it's in the same fashin as the
>> setPrototype() ?
>> It's "clean" in the sense that it's important to
>> overrides only the
>> implementation defined is in your super class,
>> guaranteeing a correct
>> overriding if different subclasses overrides the
>> same method multiple
>> time. In javascript, it's easy to directly  get the
>> implementation of
>> an of your ascendant, and bypass some !
>>
>
> Looks good. One question though... How  would this
> work with multiple overrides?
>
> example:
>
> function MyClass1(){}
> var p= dynapi.setPrototype('MyClass1','DynLayer');
> dynapi.overwrite('MyClass1','setSize');
> p.setSize=function(w,h){
>   this.superSetSize(w,h);
>    // code here
> };
>
> function MyClass2(){}
> var p= dynapi.setPrototype('MyClass2','MyClass1');
> dynapi.overwrite('MyClass2','setSize');
> p.setSize=function(w,h){
>   this.superSetSize(w,h); 	
>   // will the above superSetSize be DynLayer's or
> MyClass1 setSize function?
	The above will call MyClass1.prototype.setSize
>   // If it's MyClass1 then how will the MyClass1 code
> access DynLayer's setSize()?
	Because the overwrite method creates MyClass1.prototype.superSetSize = 
DynLayer .prototype.superSetSize

>
>    // code here
> };
>
> Also, how will it work with multiple extensions?
>
It doesn't ! There's the exact same problem with categories in 
Objective-C. If you define the same method (even for new method that 
didn't exists) on a class in 2 different source files, depending on the 
loading mechanism, either the first or the last would win.
There's no way to determine an order between the multiple definitions, 
and even if there were an order, at best you want to control which one 
wins, but defining any combining of the different implementations looks 
risky to me.
So bottom line we should decide which one wins, and stick with that.
In the implementation I did, the first one win as I check if the 
superSetSize exists, and if it does, then subsequent use overwrite 
would have no effects.
If we don't check, then the last call win. I guess, if you provide a 
extension it would be called after and you would expect it to win.

This overwrite use is meant for overriding method in subclasses. Now if 
you want to re define setSize on DynLayer with your custom 
implementation, and then have all subclasses that inherit from DynLayer 
and override setSize to use your new implementation, you really have to 
assign DynLayer.prototype.setSize = myNewSetSize

And all should be as expected. But that usage could be described as a 
"hack". The same can be done in the Objective-C run-time, but I've only 
done it once. This usage should be pretty rare, and therefore you can 
do it manually I think.

Make sense ?

Benoit

> example:
>
> // extension library #1
> dynapi.overwrite('DynLayer','setSize');
> DynLayer.prototype.setSize=function(w,h){
>    this.superSetSize(w,h);
>   // code here
> };
>
> // extension library #2 - loaded after extension #1
> dynapi.overwrite('DynLayer','setSize');
> DynLayer.prototype.setSize=function(w,h){
>    this.superSetSize(w,h);
>   // code here
> };
>
> When setSize id called will it execute code in the
> following order?
>
> object -> extension #2 setSize() -> extension #1
> setSize() -  DynLayer's orginal setSize()
>
>>> Is the term "subclass" correct or should we term
>> it as
>>> "overwrite"?
>> We should use overwrite, it's the appropriate term
>> in OO terminology
>> when a subclass modify an inherited method.
>
> Thanks
>
> --
> Raymond Irving
>
>>
>> Benoit
>>
>>>
>>> Any comments?
>>>
>>> --
>>> Raymond Irving
>>>
>>> __________________________________________________
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>
>
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