Re: Re: Re: ClassWriter#visit now final

On 11/22/2011 03:29 PM, Jochen Theodorou wrote:
> Am 17.11.2011 20:55, schrieb Eric Bruneton:
>> Jochen Theodorou wrote:
>>> Hi all,
>>>
>>> I just noticed, that ClassWriter#visit is now final. We used a
>>> ClassReader to first read a class and then write it out again with a
>>> different super class. I strongly assume the old code, in which we
>>> simple extended the class and rewrote the visit method is wrong. But 
>>> how
>>> is it done correctly then?
>>
>> you should write a subclass of ClassVisitor. The old code is "wrong" in
>> that it does not specify an API version and so backward binary
>> compatibility can not be ensured.
>
> You wrote "wrong", because before it was an interface and thus you 
> couldn't even go this way I strongly assume. But I couldn't really 
> find an explanation for that api version thing. Looking at the source 
> code:
>
>>     public ClassVisitor(final int api, final ClassVisitor cv) {
>>         /*if (api != Opcodes.ASM4) {
>>             throw new IllegalArgumentException();
>>         }*/
>>         this.api = api;
>>         this.cv = cv;
>>     }
>
> The information is stored in a protected field and then it seems to be 
> forgotten. Maybe you could explain a bit the intention? Probably it 
> was discussed here already... I didn't find that either... since you 
> changed from interface to class anyway, it cannot have anything to do 
> with asm 3.x

If you take a look to the way ASM has evolved, we break the binary 
compatibility
by example because some parameters was added to a method.
When ASM5 will be out, the API version value will help us to wire
a call to the old API to a call to the new API to provide a kind of 
emulation layer.

>
> bye blackdrag
>

cheers,
Rémi

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