From: Jacob Fugal <lukfugl@...>
Date: 2006-02-13T01:42:47+09:00
Subject: Re: [QUIZ] FasterGenerator (#66)

On 2/12/06, Luke Blanshard <luke@blanshard.us> wrote:
>     x = 1
>     g = Generator.new do |g|
>       5.times {|i| g.yield [x,i].max}
>     end
>
>     until g.end?
>       x = 10 if g.current > 2
>       puts g.next
>     end
>
> This outputs 1, 1, 2, 3, 10.
>
> The next question is, why is the API for this class so crappy?  I would
> have expected the output to be 1, 1, 2, 10, 10.  But creating the
> generator automatically advances to the first yield, and "next" advances
> to the next one while returning the previous one.  This is just wrong.

Actually, there's no way (I can think of) to get the output you
expect, and it has nothing to do with an initial advance or anything.
My implementation doesn't advance to the yields until required, yet
has the same output. This is because of these two lines:

 x = 10 if g.current > 2
 puts g.next

g.current returns the current value. g.current is not greater than two
until g.current == 3. g.next then returns the same as g.current, while
also advancing the internal counter. The behavior your describing
would require changing the value of g.current by assigning to x. Can't
be done.

Jacob Fugal