From: Marc-Andre Lafortune <ruby-core-mailing-list@...>
Date: 2011-06-23T23:43:47+09:00
Subject: [ruby-core:37323] Re: [Ruby 1.9 - Feature #4917] NilClass#to_ary

Hi,

On Wed, Jun 22, 2011 at 6:34 PM, Charles Nutter <headius@headius.com> wrote:
>
> Perhaps if an optimization is needed, it could just be adding a nil check to Kernel#Array.

Yes, that's a possibility I thought of.

The problem lies both in the "if" (note that the included benchmark
shows a ~35% performance gain) and the fact that the definition of
Array() would have to change slightly.

I also fail to see why Array(nil) should be optimized and not, say, Array(42)

I'm feel there are many more important things to worry about.

> ----------------------------------------
> Feature #4917: NilClass#to_ary
> http://redmine.ruby-lang.org/issues/4917
>
> Author: Jay Feldblum
> Status: Rejected
> Priority: Normal
> Assignee:
> Category:
> Target version:
>
>
> As a performance improvement in certain cases, nil should respond to to_ary.
>
> Kernel#Array, when passed nil, first tries to send to_ary to nil (which actually ends up calling method_missing on nil) and then tries to send to_a to nil which finally succeeds. When Kernel#Array is used often, for example in library/gem code, this can have a noticeable, if relatively small, negative impact on the overall application performance.
>
> � �$ irb
>
> � �> RUBY_VERSION
> � � => "1.9.2"
>
> � �> require 'benchmark'
> � �> def bench(times) Benchmark.bmbm{|x| x.report{times.times(&Proc.new)}} end
>
> � �# Let's zero the scale....
> � �> bench(10_000_000) { }
>
> � �# The "before" benchmark....
> � �> bench(10_000_000) { Array(nil) }
>
> � �# An optimization....
> � �> NilClass.class_eval { alias to_ary to_a }
>
> � �# The "after" benchmark....
> � �> bench(10_000_000) { Array(nil) }
> � �# Much faster!
>
> � �# Let's see how many times method_missing actually gets called....
> � �> NilClass.class_eval { undef to_ary }
> � �> class NilClass
> � �> � alias method_missing_without_hit method_missing
> � �> � def method_missing(name, *args, &block)
> � �> � � $method_missing_hits += 1
> � �> � � method_missing_without_hit(name, *args, &block)
> � �> � end
> � �> end
>
> � �> $method_missing_hits = 0
> � �> bench(100_000) { Array(nil) }
> � �# Very slow!
> � �> $method_missing_hits
> � � => 200005
>
> � �> NilClass.class_eval { alias to_ary to_a }
> � �> $method_missing_hits = 0
> � �> bench(100_000) { Array(nil) }
> � �# Instantaneous!
> � �> $method_missing_hits
> � � => 0
>
>
>
> --
> http://redmine.ruby-lang.org
>
>