[Vm-dev] Re: Method executing but not sent to the receiver

[Henrik Sperre Johansen]

On 26.04.2011 16:31, Mariano Martinez Peck wrote:
>   
>
>
>
>
> On Tue, Apr 26, 2011 at 12:50 PM, Henrik Sperre Johansen 
> <henrik.s.johansen at veloxit.no <mailto:henrik.s.johansen at veloxit.no>> 
> wrote:
>
>
>     Say you have Class A:
>     inst vars : one two three
>
>     and method compiled on it:
>     foo
>     ^one
>
>     Then you also have Class B:
>     inst vars: three two one
>
>     Then you do
>     methodFoo := A >> #foo
>     methodFoo executeWithReceiver: B new one: 1; three: 3; yourself
>     arguments:
>     #()
>
>     It'll return 3, which'll probably confuse those not very familiar
>     with the
>     bytecodes.
>
>     Or using a class with no instvars, it'll crash in a similar manner
>     to what
>     you get if you currently do:
>     Test methodDictionary at: #foo put: MCPackage >> #packageInfo.
>     Test >> #foo.
>     Test new foo
>
>
> You see, now I got it :)  I am just slow.
> Thanks Henrik for this example. In fact, it was not even obvious for 
> me until you told me. The "problem" is that the bytecodes to 
> access/set instanceVariables work by position instead of name, no?
> I mean, 'one' is never put in the literals of A >> #foo
yup, instvar access in byte codes is indexed.

>
> Nevertheless, exactly the same happens with 
> #valueWithReceiver:arguments:    so...ok, we have this problem but we 
> also have from before ;)
> right ?
Dunno, I only commented on the code you posted.
>
> solutions?
>
> First I would put a nice comment in #valueWithReceiver:arguments:   
> and #valueWithReceiver:arguments:
>
> Second, if I understood you correctly you mean to do in your previous 
> email, you want to validate that the class of the receiver is the same 
> as the class where the CompiledMethod is installed and if it is not, 
> throw an error ?
>
> On the one hand that would limit a bit the usage because that fails 
> only when there is instance var access, doesn't it?  On the other 
> hand, it prevents some crashes or weird cases where the results are 
> not the expected ones.
>
> Opinions?
Not sure if the overhead of such a check would be worth it.
The least restrictive to avoid outright crashing would probably be to 
check that instvar accessing bytescodes in the method did not exceed 
that of the receiver, but a class check would probably be simpler.

I'd be ok with just a good comment, one would expect users of this to 
sort of know what they are doing.
On the other hand, you didn't realize it untill I pointed it out 
specifically ;)

If it should be allowed at all, as per Igor's post.

I love disagreeing with myself :D

Cheers,
Henry

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