Ok, now I get it :D Thanks a lot Mariano! 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
