From: "Eregon (Benoit Daloze)" <noreply@...>
Date: 2022-12-01T22:06:55+00:00
Subject: [ruby-core:111137] [Ruby master Bug#19165] Method (with no param) delegation with *, **, and ... is slow

Issue #19165 has been updated by Eregon (Benoit Daloze).





How many allocations is it with `...` when not using forwardable but just delegation with `(...)`? I'd think 1 Array + 1 Hash.



----------------------------------------

Bug #19165: Method (with no param) delegation with *, **, and ... is slow

https://bugs.ruby-lang.org/issues/19165#change-100416



* Author: matsuda (Akira Matsuda)

* Status: Open

* Priority: Normal

* ruby -v: ruby 3.2.0dev (2022-12-01T08:05:41Z master 4e68b59431) +YJIT [arm64-darwin21]

* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

----------------------------------------

I found that method delegation via Forwardable is much slower than normal method call when delegating a method that does not take parameters.



Here's a benchmark that explains what I mean.



```

require 'forwardable'

require 'pp'

require 'benchmark/ips'



class Obj

  extend Forwardable



  attr_accessor :other



  def initialize

    @other = Other.new

  end



  def foo_without_splat

    @other.foo

  end



  def foo_with_splat(*)

    @other.foo(*)

  end



  def foo_with_splat_with_name(*args)

    @other.foo(*args)

  end



  def foo_with_splat_and_double_splat(*, **)

    @other.foo(*, **)

  end



  def foo_with_triple_dots(...)

    @other.foo(...)

  end



  delegate :foo => :@other

end



class Other

  def foo() end

end



o = Obj.new



Benchmark.ips do |x|

  x.report 'simple call' do

    o.other.foo

  end



  x.report 'delegate without splat' do

    o.foo_without_splat

  end



  x.report 'delegate with splat' do

    o.foo_with_splat

  end



  x.report 'delegate with splat with name' do

    o.foo_with_splat_with_name

  end



  x.report 'delegate with splat and double splat' do

    o.foo_with_splat_and_double_splat

  end



  x.report 'delegate with triple dots' do

    o.foo_with_triple_dots

  end



  x.report 'delegate via forwardable' do

    o.foo

  end

end





(result)

         simple call     38.918M (� 0.9%) i/s -    194.884M

delegate without splat

                         31.933M (� 1.6%) i/s -    159.611M

 delegate with splat     10.269M (� 1.6%) i/s -     51.631M

delegate with splat with name

                          9.888M (� 1.0%) i/s -     49.588M

delegate with splat and double splat

                          4.117M (� 0.9%) i/s -     20.696M

delegate with triple dots

                          4.169M (� 0.9%) i/s -     20.857M

delegate via forwardable

                          9.204M (� 2.1%) i/s -     46.295M

```



It shows that Method delegation with a splat is 3-4 times slower (regardless of whether the parameter is named or not), and delegation with a triple-dot literal is 9-10 times slower than a method delegation without an argument.

This may be because calling a method taking a splat always assigns an Array object even when no actual argument was given, and calling a method taking triple-dots assigns five Array objects and two Hash objects (this is equivalent to `*, **`).





Are there any chance reducing these object assignments and making them faster? My concern is that the Rails framework heavily uses this kind of method delegations, and presumably it causes unignorable performance overhead.







-- 

https://bugs.ruby-lang.org/

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