From: Robert Klemme <bob.news@...>
Date: 2004-12-08T22:57:42+09:00
Subject: Re: Using yield


"David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
news:Pine.LNX.4.61.0412080544030.25964@wobblini...
> Hi --
>
> On Wed, 8 Dec 2004, Robert Klemme wrote:
>
> >
> > "David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
> > news:Pine.LNX.4.44.0412071110500.21344-100000@wobblini...
> >> Hi --
> >>
> >> On Tue, 7 Dec 2004, Robert Klemme wrote:
> >>
> >>> 13:21:36 [robert.klemme]: ruby yield-vs-block.rb
> >>>                           user     system      total        real
> >>> yield                 0.250000   0.000000   0.250000 (  0.249000)
> >>> block                 0.125000   0.000000   0.125000 (  0.124000)
> >>> 13:21:44 [robert.klemme]: cat yield-vs-block.rb
> >>>
> >>> require 'benchmark'
> >>> include Benchmark
> >>>
> >>> REP = 100000
> >>>
> >>> def bl_yield(n)
> >>>   n.times {|i| yield i}
> >>> end
> >>>
> >>> def bl_fwd(n,&b)
> >>>   n.times(&b)
> >>> end
> >>
> >> Those aren't equivalent, though.  The second one would have to be:
> >>
> >>   n.times {|i| b.call(i) }
> >>
> >> to compare the two idioms directly.
> >
> > Hm, I'm not sure I agree here.  My point was to compare performance of
two
> > idioms achieving that a block handed to a method is called from
another
> > method called within that method.  You are right with respect to the
> > invocation chain though.
>
> I think we're talking about different sets of "two idioms",

Yes, we are / were. :-)

> but I see
> what you mean about your set.  As for....
>
> >> Or am I behind the times on automatic propagation?  (But even in that
> >> case I don't think supplying block #1 to method #2 is the same as
> >> yielding to block #1 during method #1.)
> >
> > What exactly do you think is the difference here?  (Apart from
performance
> > of course)
>
> .. there's something nagging in my mind that I can't quite nail down,
> having something to do with argument parsing, I think.  It's probably
> illusory.  If I manage to figure out what it is, I'll post it :-)

Thanks!  I'm curios to learn what you find out.  Wait...

If the other method (Fixnum#times in my example) would do different
yielding.  Hm...  I think I should redefine my set:

14:52:25 [09_Public]: ruby yield-vs-block.rb
                          user     system      total        real
yield                 0.265000   0.000000   0.265000 (  0.263000)
yield_star            0.766000   0.000000   0.766000 (  0.778000)
block                 0.109000   0.000000   0.109000 (  0.124000)
14:52:58 [09_Public]: cat yield-vs-block.rb

require 'benchmark'
include Benchmark

REP = 100000

def bl_yield(n)
  n.times {|i| yield i}
end

def bl_yield_star(n)
  n.times {|*i| yield *i}
end

def bl_fwd(n,&b)
  n.times(&b)
end

bm(20) do |b|
  b.report("yield") do
    bl_yield(REP) {|i| i + 1}
  end

  b.report("yield_star") do
    bl_yield_star(REP) {|i| i + 1}
  end

  b.report("block") do
    bl_fwd(REP) {|i| i + 1}
  end
end

Uh, even worse performance for "yield *i". *shudder*  But not really
unexpected.  One more reason to use &b for forwarding.

Kind regards

    robert