What is the fastest way to add one thing to an array without mutating the array?

benchmark_append.rb

require 'benchmark/ips'

a = (0..10).to_a

Benchmark.ips do |x|
  x.report("push")      { a.dup.push(100) }
  x.report("shovel")    { a.dup << 100 }
  x.report("concat")    { a.dup.concat([100]) }
  x.report("+")         { a + [100] }
  x.report("unshift")   { a.dup.unshift(100) }
  x.report("insert -1") { a.dup.insert(-1, 100) }
  x.report("insert 0")  { a.dup.insert(0, 100) }
  x.report("[]=")       { b = a.dup ; b[0,0] = 100 }
  x.report("|")         { a | [100] }

  x.report("nil") { nil }
end

Add x.compare!