array_to_hash.rb

require 'benchmark'
require 'benchmark/ips'

seed = [1,2,3]
map_proc = ->(i){ [i,i] }

Benchmark.ips do |x|
  x.report('inject') { seed.inject({}){ |mem, i| mem[i]=i; mem } }
  x.report('to_h') { seed.map(&map_proc).to_h }
  x.report('Hash[map]') { Hash[seed.map(&map_proc)] }
  x.report('Hash[*flat_map]') { Hash[*seed.flat_map(&map_proc)] }
  x.report('lazy.to_h') { seed.lazy.map(&map_proc).to_h }
end

output.txt

Warming up --------------------------------------
              inject    74.295k i/100ms
                to_h    78.415k i/100ms
           Hash[map]    73.396k i/100ms
     Hash[*flat_map]    55.862k i/100ms
           lazy.to_h    14.441k i/100ms
Calculating -------------------------------------
              inject    946.430k (± 3.0%) i/s -      4.755M in   5.029162s
                to_h    970.956k (± 3.5%) i/s -      4.862M in   5.013636s
           Hash[map]    894.628k (± 4.6%) i/s -      4.477M in   5.016057s
     Hash[*flat_map]    644.230k (± 3.9%) i/s -      3.240M in   5.037430s
           lazy.to_h    149.488k (± 2.2%) i/s -    750.932k in   5.025786s