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