From: Eric Armstrong <Eric.Armstrong@...>
Date: 2006-05-16T11:08:44+09:00
Subject: Re: learn to program

That's a nice little visualization trick. Did you
come up with that?

Logan Capaldo wrote:
> 
> On May 15, 2006, at 6:05 PM, corey konrad wrote:
> 
>> I realy dont understand what Chris is talking about here in his book
>> "learning to program" Can someoe shed some light on this
>>
>> def little_pest tough_var
>> tough_var = nil
>> puts ' HAHA! I ruined your variable!'
>> end
>>
>> tough_var = ' You can\' t even touch my variable!'
>> little_pest tough_var
>> puts tough_var
>>
>> output:
>> HAHA! I ruined your variable!
>> You can' t even touch my variable!
>>
>> excerpt from his book:
>> In fact, two variables in that little program are named tough_var:
>> one inside little_pest and one outside of it. They don�t communicate.
>> They aren�t related. They aren�t even friends. When we called
>> little_pest tough_var, we really just passed the string from one
>> tough_var to the other (via the method call, the only way they can even
>> sort of communicate) so that both were pointing to the same string.
>> Then little_pest pointed its own local tough_var to nil, but that
>> did nothing to the tough_var variable outside the method.
>>
>> --Posted via http://www.ruby-forum.com/.
>>
> 
> It has to do with variable scoping. Try this metaphor on for size.
> 
> You have a stack of papers. When ever you call a function, you grab a 
> blank piece of paper. On it, you write the names and values for all the 
> variables in that function and you put it on top of the stack. You then 
> execute the code inside the function. Any code in the function can only 
> change the stuff written on the piece of paper at the top of the stack. 
> When the function finishes, we take it's piece of paper off the top of 
> the stack of papers and throw it away.
> 
> Ok so we have an initial piece of paper.
> 
> We write on it:
> tough_var = ' You can\' t even touch my variable!'
> 
> then we call a function, little_pest. We grab a blank piece of paper for 
> little pest, and write on it
> tough_var = ' You can\'t even touch my variable!'
> 
> we put it on top of the stack.
> 
> Then little_pest says to set tough_var to nil.
> 
> We look at our piece of paper on the top of the stack of papers, 
> scribble out tough_var and write
> tough_var = nil
> 
> We then print the "HAHA!" message, and finish our function. Since we are 
> done with our function, we take the piece paper off the top of the 
> stack, crumple it up, and throw it away.
> 
> then we saee we must print tough_var. We look at the paaper on the top 
> of the stack to see what tough var means. Oh its a string with ' You 
> can\'t touch my variable '. Ok, we print that.
> 
>