From: "Thomas B." <tpreal@...>
Date: 2008-09-21T06:51:55+09:00
Subject: Re: Explaination of a bit of code

Dave Lenhardt wrote:
> I guess I am having trouble thinking how this would work out.  Each is
> suppose to go through a set of items.  however, where are the items?  I
> see three strings but they are used in yield statements.  How is this
> method actually working?

The method each is working just as you programme it. For Arrays (and 
Enumerables, in general) it calls the passed block with each element of 
the object (self) in turn, so in some useless pseudocode, Array#each 
works like this:
for each element of self in e
  yield(e)
end
Now you can see that your own each works just like
["Classical","Jazz","Rock"].each{|e| yield(e)}
So, your Periods::new works like the array ["Classical","Jazz","Rock"] 
itself. Only your object is a dummy array - it does not read the 
elements from any kind of set or anything, it is just hardcoded to call 
yield with these three strings. But from outside you cannot tell your 
Period::new from ["Classical","Jazz","Rock"], they just behave in the 
same way when we call the method each on them. And that's why the for 
loop sees your object as if it was the array of the three strings.

TPR.
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