On Wed, Oct 12, 2011 at 6:00 PM, Clara Allende <[email protected]>wrote:
> Ok, now I get it :D Thanks a lot Mariano! > > No problem :) > > On 12 October 2011 12:49, Mariano Martinez Peck <[email protected]>wrote: > >> >> >> On Wed, Oct 12, 2011 at 5:38 PM, Levente Uzonyi <[email protected]> wrote: >> >>> On Wed, 12 Oct 2011, Clara Allende wrote: >>> >>> Hi guys, >>>> >>>> I'm wondering, why? >>>> >>>> ProtoObject>> ~~ anObject >>>> "Answer whether the receiver and the argument are not the same object >>>> (do not have the same object pointer)." >>>> >>>> self == anObject >>>> ifTrue: [^ false] >>>> ifFalse: [^ true] >>>> >>>> >> Hi Carla. I can think about two things. The first one, is the one Levente >> said, performance. >> If you analyze the bycode of this method, you will see that it is >> extremely fast because: >> >> 1) #== has an special associated bytecode, that is, them VM maps such >> bytecode to an specific primitive and it is directly executed. It means that >> the method #== is really never sent. >> 2) ifTrue:ifFalse: is also optimized (inlined) by the compiler. Again, it >> method is never executed and instead the compiler replace a message send >> bytecode with jump ones. >> >> Another possible reason (it may not be the case, but in another places it >> is), is to prevent VM interruption for check other processes. In summary, >> the VM checks whether it should execute another process of the queue after a >> method execution. As you know, some parts of the scheduling process is done >> at the image side. And from there we lack a way to say to the VM, "please >> execute this method without checking others processes". Hence, in a few yet >> very specific places of PRocess, Scheduler, Semaphore, etc, #== is used as a >> mean of executing something WITHOUT being interrupted. I can imagine that it >> may happen the same with #~~. So if you implement such method with a #not, >> you will indeed send a message, proving a possibilty to be interrupted. >> >> Another reasons, similar to the previous one, is that sometimes #== is >> also used as a way to avoid executing method. So..there are some methods (I >> don't remember if #allInstancesDo: or #allObjectsDo:) will loop forever >> because the loop condition would be creating objects (remember that method >> execution creates objects such as MethodContext). >> So...again, I think it may happen the same with #~~. >> >> That being said, I agree that the method deserve a GOOD comment explaining >> the reasons of such optimization. >> >> Cheers >> >> >> >>> Instead of: >>>> ProtoObject>> ~~ anObject >>>> "Answer whether the receiver and the argument are not the same object >>>> (do not have the same object pointer)." >>>> >>>> ^(self == anObject) not >>>> >>>> And why? >>>> Object >> ~= anObject >>>> "Answer whether the receiver and the argument do not represent the >>>> same object." >>>> >>>> ^self = anObject == false >>>> >>>> Instead of >>>> Object>> ~= anObject >>>> "Answer whether the receiver and the argument do not represent the >>>> same object." >>>> >>>> ^(self = anObject) not. >>>> >>>> Is there any particular reason for this that I'm missing? >>>> >>> >>> Performance. >>> >>> >>> Levente >>> >>> Thanks in advance! >>>> -- >>>> >>>> "*Most good programmers do programming not because they expect to get >>>> paid >>>> or get adulation by the public, but because it is fun to program.*" >>>> >>>> Linus Torvalds >>>> >>>> >>> >> >> >> -- >> Mariano >> http://marianopeck.wordpress.com >> >> > > > -- > > "*Most good programmers do programming not because they expect to get paid > or get adulation by the public, but because it is fun to program.*" > > Linus Torvalds > > > -- Mariano http://marianopeck.wordpress.com
