jruby (9.2.9.0 dev)
 unpack early return    700.842k (± 7.8%) i/s -      3.485M in   5.012230s
        unpack block      2.289M (± 9.2%) i/s -     11.253M in   4.992273s
        unpack first      2.853M (± 5.8%) i/s -     14.189M in   4.994309s

jruby + indy (9.2.9.0 dev)
 unpack early return    923.728k (±10.2%) i/s -      4.545M in   4.987390s
        unpack block      2.914M (± 9.3%) i/s -     14.266M in   4.985981s
        unpack first      3.770M (± 7.0%) i/s -     18.699M in   4.991746s

jruby + indy + graal (9.2.9.0 dev)
 unpack early return    348.480k (±10.8%) i/s -      1.720M in   5.013014s
        unpack block      2.973M (±10.6%) i/s -     14.613M in   4.995835s
        unpack first      4.495M (± 7.3%) i/s -     22.248M in   4.990273s

ruby (2.5.3)
 unpack early return      2.212M (± 9.2%) i/s -     10.946M in   5.000249s
        unpack block      2.688M (± 5.4%) i/s -     13.407M in   5.007471s
        unpack first      2.868M (± 4.1%) i/s -     14.313M in   5.001607s

ruby (2.7 dev)
 unpack early return      2.698M (± 7.2%) i/s -     13.406M in   5.008788s
        unpack block      3.253M (± 5.6%) i/s -     16.222M in   5.010958s
        unpack first      2.974M (± 5.1%) i/s -     14.827M in   5.007237s

ruby + jit (2.7 dev)
 unpack early return      2.783M (± 5.3%) i/s -     13.902M in   5.014952s
        unpack block      3.941M (± 9.2%) i/s -     19.537M in   5.007289s
        unpack first      3.444M (± 8.5%) i/s -     17.083M in   5.006996s

truffleruby (19.0.0)
 unpack early return      5.583M (±28.9%) i/s -     21.127M in   5.003905s
        unpack block     10.755M (±14.5%) i/s -     48.633M in   5.147068s
        unpack first      7.976M (±18.9%) i/s -     33.639M in   4.990572s

require 'benchmark/ips'

STRING = "".freeze

def unpack_block
  STRING.unpack('m') { |x| return x }
end

def unpack_block2
  value = nil
  STRING.unpack('m') { |x| value ||= x }
  value
end

def unpack_first
  STRING.unpack('m').first
end

Benchmark.ips do |x|
  x.report('unpack early return') { unpack_block  }
  x.report('unpack block')        { unpack_block2 }
  x.report('unpack first')        { unpack_first  }
end