Benchmark #flat_map() and flatten.map() in different ruby versions

bench.rb

require 'benchmark/ips'

def flatmap
  [[1,2],[3,4]].flat_map {|i| i }
end

def flatten_then_map
  [[1,2],[3,4]].flatten.map {|i| i }
end

Benchmark.ips do |x|

  x.report('flatmap') { flatmap }

  x.report('flatten_then_map') { flatten_then_map }

  x.compare!
end

console-output

le_daf@macbook-pro-de-damien ~/projects/stackbuilders/haystak/dynamic (feature/hk2475-integrate-styleguide-for-providers●●)$ RBENV_VERSION=2.0.0-p576 ruby bench.rb     [2.0.0-p576]
Warming up --------------------------------------
             flatmap    36.053k i/100ms
    flatten_then_map    22.249k i/100ms
Calculating -------------------------------------
             flatmap    548.515k (± 4.7%) i/s -      2.740M
    flatten_then_map    311.757k (± 8.1%) i/s -      1.557M

Comparison:
             flatmap:   548515.3 i/s
    flatten_then_map:   311757.4 i/s - 1.76x slower

le_daf@macbook-pro-de-damien ~/projects/stackbuilders/haystak/dynamic (feature/hk2475-integrate-styleguide-for-providers●●)$ RBENV_VERSION=2.2.3 ruby bench.rb          [2.0.0-p576]
Warming up --------------------------------------
             flatmap    45.096k i/100ms
    flatten_then_map    26.296k i/100ms
Calculating -------------------------------------
             flatmap    880.410k (± 3.5%) i/s -      4.419M
    flatten_then_map    387.535k (± 3.5%) i/s -      1.946M

Comparison:
             flatmap:   880409.6 i/s
    flatten_then_map:   387534.5 i/s - 2.27x slower