From: Robert Klemme <bob.news@...>
Date: 2004-12-08T23:22:30+09:00
Subject: Re: Using yield


"David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
news:Pine.LNX.4.61.0412080603510.9910@wobblini...
> On Wed, 8 Dec 2004, Robert Klemme wrote:
>
> > 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.
>
> I think my vague concern about argument parsing has to do with the
> question of who gets to decide.  There might be a case where for some
> reason you wanted to do:
>
>    def some_method(n)
>      n.times {|*i| yield i}
>    end
>
> or something weird like that... but I guess that takes us away from
> exact equivalence with &b, since now I'm not just passing the args to
> yield one at a time as they come.

Yeah, the &equivalent would be

   def some_method(n,&b)
     n.times {|*i| b.call(i)}
   end

which suffers a similar detour as the yield approach.  I think the most
common case for "block forwarding" does not involve argument mangling so
this is probably a special case.

Kind regards

    robert