[ruby-core:100079] [Ruby master Feature#4917] NilClass#to_ary

Issue #4917 has been updated by DanRathbun (Dan Rathbun).


y_feldblum (Jay Feldblum) wrote in #note-6:
> This minor performance issue becomes a huge problem when NilClass#method_missing is defined, such as in ActiveSupport (https://github.com/rails/rails/blob/master/activesupport/lib/active_support/whiny_nil.rb), which is a popular choice when developing a Rails application.
> 

I'm curious, now that Ruby 2.x has refinements (and we're near 10 years on,) would there be acceptable speed improvements using refinements rather than direct-patching (ie, hacks) ?

----------------------------------------
Feature #4917: NilClass#to_ary
https://bugs.ruby-lang.org/issues/4917#change-87636

* Author: y_feldblum (Jay Feldblum)
* Status: Rejected
* Priority: Normal
----------------------------------------
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




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