Compare map vs map!

benchmark.rb

key = "id".freeze
rows = []
5000.times { rows << {"id" => rand(5000).to_s} }


require 'benchmark/ips'

Benchmark.ips do |x|
  x.report('map') { rows.dup.map { |r| r[key].to_i } }
  x.report('map!') { rows.dup.map! { |r| r[key].to_i } }
  x.compare!
end

require 'benchmark/memory'

Benchmark.memory do |x|
  x.report('map') { rows.dup.map { |r| r[key].to_i } }
  x.report('map!') { rows.dup.map! { |r| r[key].to_i } }
  x.compare!
end

Calculating -------------------------------------
                 map    963.373  (± 3.7%) i/s -      4.888k in   5.081362s
                map!    996.699  (± 4.8%) i/s -      5.050k in   5.079215s

Comparison:
                map!:      996.7 i/s
                 map:      963.4 i/s - same-ish: difference falls within error

Comparison:
                map!:      40040 allocated
                 map:      40080 allocated - 1.00x more