From: 7stud -- <dolgun@...>
Date: 2007-09-24T13:22:47+09:00
Subject: Re: how to add an iterator to a class?

Mike Steiner wrote:
> 
> So my question is: How do I replace GetArray with something more 
> elegant,
> that gives MyArray a method named .each that I can call directly?
> 

each() is an "iterator".  An iterator is a method that uses a "yield 
statement".  A yield statement acts similar to a method call, and looks 
like this:

yield some_val

yield calls the block and sends it the argument specified to the right 
of 'yield'.  The method that contains the yield statement, i.e. each(), 
halts and waits for the block to finish executing, and then execution 
continues in the method.  That interaction is very similar to a method 
that calls another method:

def greet
    sleep(2)
    puts "hello"
    sleep(5)
end

def start
    greet

    x = 10
    puts x
end

start

If you run that code, you'll see that the method start() waits for 
greet() to finish executing before it outputs 10.  yield works 
similarly: execution does not continue in the method that contains the 
yield statement, e.g. each(), until the block that the yield statement 
called finishes executing.

So, you need to define a method called each, and inside each you are 
going to use a yield statement that sends values to a block.  What 
values?  The values are the elements of your array.  Since you are 
generally going to need to yield more than one value, i.e. your array 
will have more than one element in it, you can put your yield statement 
inside a loop:


class MyArray
    def initialize
        @a = Array.new
    end
    def push( item )
        @a.push( item )
    end

    def each
        count = 0
        while elmt = @a[count]
            yield elmt
            count += 1
        end
    end

end

arr = MyArray.new
arr.push(1)
arr.push(2)
arr.push(3)

arr.each{|elmt| puts elmt +2}
-- 
Posted via http://www.ruby-forum.com/.