Object Allocation in Ruby kwargs

kwargs_allocation.rb

require 'allocation_tracer'
require 'active_support/core_ext/array/extract_options'
require 'pp'

# Active Support
def foo1(options = {})
  options[:x] || 1
end

# Ruby
def foo2(x: 1)
  x
end

# Active Support, varargs
def bar1(*args)
  options = args.extract_options!
  options[:y] || 1
end

# Ruby, varargs
def bar2(*args, y: 1)
  y
end

ObjectSpace::AllocationTracer.setup(%i{path line type})


foo1 x: 2
foo2 x: 2
bar1 y: 2
bar2 y: 2

pp activesupport_1: ObjectSpace::AllocationTracer.trace {
  foo1 x: 2
}
pp kwargs_1: ObjectSpace::AllocationTracer.trace {
  foo2 x: 2
}

pp activesupport_2: ObjectSpace::AllocationTracer.trace {
  bar1 y: 2
}
pp kwargs_2: ObjectSpace::AllocationTracer.trace {
  bar2 y: 2
}

result

# ruby 2.1.10p492 (2016-04-01 revision 54464) [x86_64-darwin15.0]

{:activesupport_1=>{["kwargs_allocation.rb", 31, :T_HASH]=>[1, 0, 0, 0, 0, 0]}}
{:kwargs_1=>{["kwargs_allocation.rb", 34, :T_HASH]=>[2, 0, 0, 0, 0, 0]}}
{:activesupport_2=>
  {["kwargs_allocation.rb", 38, :T_HASH]=>[1, 0, 0, 0, 0, 0],
   ["kwargs_allocation.rb", 38, :T_ARRAY]=>[1, 0, 0, 0, 0, 0]}}
{:kwargs_2=>
  {["kwargs_allocation.rb", 41, :T_HASH]=>[2, 0, 0, 0, 0, 0],
   ["kwargs_allocation.rb", 41, :T_ARRAY]=>[1, 0, 0, 0, 0, 0]}}

# ruby 2.2.7p470 (2017-03-28 revision 58194) [x86_64-darwin15]..ruby 2.5.0dev (2017-05-19 trunk 58790) [x86_64-darwin15]

{:activesupport_1=>{["kwargs_allocation.rb", 31, :T_HASH]=>[1, 0, 0, 0, 0, 0]}}
{:kwargs_1=>{}}
{:activesupport_2=>
  {["kwargs_allocation.rb", 38, :T_HASH]=>[1, 0, 0, 0, 0, 0],
   ["kwargs_allocation.rb", 38, :T_ARRAY]=>[2, 0, 0, 0, 0, 0]}}
{:kwargs_2=>{["kwargs_allocation.rb", 41, :T_ARRAY]=>[1, 0, 0, 0, 0, 0]}}