Re: [Pharo-users] Java "this" against our "thisContext"

[Ben Coman]

Sergi Reyner wrote: 2014-03-25 10:30 GMT+00:00 Benjamin <benjamin.vanryseghem.ph...@gmail.com>: Within an instance method or a constructor, this is a reference to the current object — the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this. from: http://docs.oracle.com/javase/tutorial/java/javaOO/thiskey.html   thisContext in smalltalk points to the execution context of the method being currently evaluated. So definitely this and self are the “same” (as long as we do not talk about inner classes) Yeah, that part I truly understand.I do know enough Java and Smalltalk to understand that "this" and "self" are equivalent (topic which somehow evaporated from the debate, and replaced with "this is the same and thisContext because [unintelligible Java code]".   thisContext does not exist in Java AFAIK That´s exactly what my intuition led me to. But when I tried to explain that I, too, don´t think that Java has a concept of "thisContext" I was presented with this: Field a = sun.misc.VM.class.getDeclaredField("directMemory"); a.setAccessible(true); a.get(null); Which, after some investigation, and as far as I understood, looks to me as if all it does is retrieve what "this" points to. It´s not really relevant because what I was arguing is that Smalltalk reflection operates at a higher level, which that piece of code proves pretty nicely, but since we got there I´d like to understand everything argued. Cheers, Sergi PS: Note that I´m not trying to win an internet debate, but simply to understand :) First required reading.... https://xkcd.com/386/ Second required reading... http://paulgraham.com/avg.html Skip down the section "The Blub Paradox" Now having said that :)  even though I'm not an expert in either Java or Smalltalk, I'm happy to have a crack (and learn something in the process where I'm wrong) You might not need to win the debate, but some examples might be useful. First showing how /this/ & /thisContext/ are different while /this/ & /self/ are the same. Object subclass: #ContextExampleA. ContextExampleA subclass: #SubA. ContextExampleA>>whoAreYou     ^ 'I am A'. SubA>> whoAreYou     ^ 'I am SubA'. ContextExampleA>> report1     Transcript show: self whoAreYou. ContextExampleA>> report2     Transcript show: thisContext whoAreYou. ---------------- So evaluating...    MySuper new report1.    MySub new report1 outputs... I am A I am SubA and evaluating...        MySuper new report2 produces Error - /thisContext/ does not understand message #whoAreYou --------------- Object subclass: #ContextExampleB. Object subclass: #ContextExampleC. ContextExampleB>>whoAreYou     ^ 'I am B'. ContextExampleC>>whoAreYou     ^ 'I am C'. ContextExampleA >> reportA     ContextExampleB new reportB. ContextExampleB >> reportB     ContextExampleC new reportC. ContextExampleC >> reportC     | context |     context := thisContext.     3 timesRepeat:     [     Transcript                 show: context printString ;                 tab ;                 show: context receiver whoAreYou;                 cr.         context := context sender.     ].     thisContext inspect. ---------- So that evaluating...       ContextExampleA new reportA outputs... ContextExampleC>>reportC    I am C ContextExampleB>>reportB    I am B ContextExampleA>>reportA    I am A ----------- Here the execution call stack has been traversed to send a message to a receiver a few levels down.  I'm not sure of the practical utility of that, but how would Java do a similar thing? cheers -ben