require "benchmark/ips" RANGE = (0..100_000) def fast array = [] RANGE.each { |number| array.concat([number]) } end def slow array = [] RANGE.each { |number| array += [number] } end Benchmark.ips do |x| x.report("Array#concat") { fast } x.report("Array#+") { slow } x.compare! end 

ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-darwin18] Warming up -------------------------------------- Array#concat 5.000 i/100ms Array#+ 1.000 i/100ms Calculating ------------------------------------- Array#concat 62.530 (±11.2%) i/s - 310.000 in 5.037308s Array#+ 0.194 (± 0.0%) i/s - 1.000 in 5.155399s Comparison: Array#concat: 62.5 i/s Array#+: 0.2 i/s - 322.37x slower