From: Ross Bamford <rossrt@...>
Date: 2006-05-14T02:24:11+09:00
Subject: Re: Making sense of the various Ruby "eval"s

On Sat, 2006-05-13 at 14:52 +0900, Eli Bendersky wrote:
> ts wrote:
> >>>>>> "E" == Eli Bendersky <eliben@gmail.com> writes:
> > 
> > E> I'm struggling to fully understand the difference between the block 
> > and
> > E> the string versions ?
> > 
> >  the string version is evil :-)
> > 
> [...]
> The way I see it, the block version is simply a convenience, making the 
> code cleaner. It is similar to wrapping a string into a single 
> (non-interpolating) quote:

As well as the difference in when the code is parsed mentioned in
another post, it's probably worth noting that string eval is slower than
block eval:

$ cat eval_bench2.rb
require 'benchmark'
o = Object.new
Benchmark.bm(10) do |b|
  b.report("eval str:") { 10000.times {o.instance_eval '10.times { |i| l = 300 * i }' }}
  b.report("eval blk:") { 10000.times {o.instance_eval { 10.times { |i| l = 300 * i }} }}
end

$ ruby -v eval_bench2.rb
ruby 1.8.4 (2005-12-24) [i686-linux]
                user     system      total        real
eval str:   0.340000   0.000000   0.340000 (  0.416134)
eval blk:   0.160000   0.000000   0.160000 (  0.203212)

In yarv, the difference is even more marked, and from what I can gather
it's likely to stay that way:

$ ruby-yarv -v eval_bench2.rb
ruby 2.0.0 (Base: Ruby 1.9.0 2006-04-08) [i686-linux]
YARVCore 0.4.0 Rev: 497 (2006-05-07) [opts: ]
                user     system      total        real
eval str:   0.820000   0.020000   0.840000 (  0.836336)
eval blk:   0.060000   0.000000   0.060000 (  0.105170)

-- 
Ross Bamford - rosco@roscopeco.REMOVE.co.uk