From: dblack@...
Date: 2007-08-07T04:45:37+09:00
Subject: Re: yield or call?

Hi --

On Tue, 7 Aug 2007, Phlip wrote:

>>> Yes, but not in the helper method. In the code I've shown there's
>>> always a block passed to the helper method. Phlip has a point here.
>>
>> That's very easy to solve:
>
> What about the two kinds of performance? Programmer performance and
> program performance?
>
> This permits only one (DRY) call to y:
>
>>       y { yield if block_given? }
>
> So is it performant? Note someone here asserted that yield was faster,
> so are these constructions still faster than a brute-force 'block.call
> if block' ?
>
> When I see 'if block' I think of comparing the RVALUE type field to
> nil or false. Just a bit mask.

Here are some benchmarks, for the two conditionals with and without a
block:

david-a-blacks-computer:~/hacking dblack$ cat yi.rb
require 'benchmark'
include Benchmark

def x(&b)
   b.call if b
end

def y
   yield if block_given?
end


n = 1000000

bmbm do |b|
   b.report("b") { n.times { x { } } }
   b.report("y") { n.times { y { } } }
   b.report("b-no block") { n.times { x } }
   b.report("y-no block") { n.times { y } }
end
david-a-blacks-computer:~/hacking dblack$ ruby yi.rb 
Rehearsal ----------------------------------------------
b            3.780000   0.010000   3.790000 (  3.798711)
y            0.700000   0.000000   0.700000 (  0.695756)
b-no block   0.350000   0.000000   0.350000 (  0.351118)
y-no block   0.380000   0.000000   0.380000 (  0.390713)
------------------------------------- total: 5.220000sec

                  user     system      total        real
b            3.810000   0.000000   3.810000 (  3.846940)
y            0.700000   0.010000   0.710000 (  0.760668)
b-no block   0.350000   0.000000   0.350000 (  0.353762)
y-no block   0.390000   0.000000   0.390000 (  0.390436)

So if the test is negative, there's not a huge difference; the
difference mainly comes when there is a block.


David

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