[ruby-core:37301] [Ruby 1.9 - Feature #4917] NilClass#to_ary

Issue #4917 has been updated by Charles Nutter.


Perhaps if an optimization is needed, it could just be adding a nil check to Kernel#Array.
----------------------------------------
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