From: Robert Klemme <bob.news@...>
Date: 2004-12-08T16:42:30+09:00
Subject: Re: Using yield


"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.

> When I make that change I get:
>
> yield                 0.320000   0.000000   0.320000 (  0.332194)
> block                 0.460000   0.000000   0.460000 (  0.490299)
>
>
> > I blieve the yield forwarding is slower because there is one more
call.
> >
> > > Wouldn't the &block form be more clutter?  Well, not that it's so
> > > much clutter in either case, but I think it would be slightly
wordier
> > > (def five_time(&block) etc.)
> >
> > For forwarding I prefer &b because the original block is simply passed
on
> > vs. a new block yields to the original block.  That seems awkward to
me
> > and seems to be slower, too.  Personally I find the yield forwarding
more
> > clutter.  YMMV
>
> The clutter point was (at least in my mind :-) strictly about the
> difference between:
>
>    def x
>      yield
>    end
>
> and
>
>    def x(&b)
>      b.call
>    end
>
> As for forwarding a block to a new method -- isn't &b the only way?

Strictly speaking yes.  But the idiom presented in my bl_yield() achieves
about the same.  At least there are no semantic differences I'm aware of.

> 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)

Kind regards

    robert