From: Brian Candler <b.candler@...>
Date: 2008-09-22T19:42:24+09:00
Subject: Re: for or each?

Sylvain Joyeux wrote:
> Nope. each { } needs one new scope for each iteration

By 'scope' do you mean 'stack frame'?

Take this trivial example:

  def each1
    yield 1
    yield 2
    yield 3
  end
  each1 { :dummy }

The only 'objects' being created here are stack frames, by the yield 
statements calling the block. To make it more explicit,

  def each2(&blk)
    blk.call(1)
    blk.call(2)
    blk.call(3)
  end
  each2 { :dummy }

Now, if you are arguing that the above code creates three objects which 
need to be garbage-collected later, then you're also arguing that the 
sequence

   foo(1)
   foo(2)
   foo(3)

creates three objects which need to be garbage-collected, and therefore 
that the loop

  for i in (1..3)
    foo(i)
  end

also creates three garbage objects.

I don't believe that's the case. I would imagine that the stack runs as, 
well, a stack. (It's not quite that simple when you get into creating 
closures of course, but if you call a closure 1000 times, you're not 
creating 1000 new closures)

Am I missing something?

Finally, I tried some simple measurements.

$ time ruby -e 'a = (1..5_000_000).to_a; a.each { :dummy }'
$ time ruby -e 'a = (1..5_000_000).to_a; for i in a; :dummy; end'

Under ruby 1.8.6p114, I find the first is about 5% faster.

Under ruby 1.8.4 (Ubuntu Dapper), I find the first is about 25% faster.

This is on relatively old Pentium machines though.
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