hash_self_merge_with_block_vs_map_then_hash_bm.rb

require "benchmark/ips"

class Test
  def initialize(test_value)
    @test_value = test_value

    assert_equal(self_merge_with_block(@test_value), map_then_hash(@test_value))
  end

  def self_merge_with_block(hsh)
    hsh.merge(hsh) {|_, val| val * 2 }
  end

  def map_then_hash(hsh)
    Hash[ hsh.map {|key, val| [ key, val * 2 ] } ]
  end

  def perform
    Benchmark.ips do |x|
      x.report("self_merge_with_block") { self_merge_with_block(@test_value) }
      x.report("map_then_hash") { map_then_hash(@test_value) }
      x.compare!
    end
  end

  def assert_equal(a, b)
    return if a == b
    raise "Expected arguments to be equal"
  end
end

Test.new(Hash[ ('aa'..'dv').zip(0..99) ]).perform

result.txt

Calculating -------------------------------------
self_merge_with_block
                          1965 i/100ms
       map_then_hash      2313 i/100ms
-------------------------------------------------
self_merge_with_block
                        21586.4 (±26.3%) i/s -     98250 in   5.020320s
       map_then_hash    23468.8 (±2.2%) i/s -     117963 in   5.028741s

Comparison:
       map_then_hash:    23468.8 i/s
self_merge_with_block:   21586.4 i/s - 1.09x slower