Ruby each vs each_with_object vs inject

bench.rb

require 'benchmark'

size = 100
list = []
size.times { |i| list << {name: "item #{i}"} }

n = 5000
Benchmark.bmbm(16) do |bm|
  bm.report('each_with_object') { n.times { list.each_with_object({}) { |item, map| map[item[:name]] = item } } }
  bm.report('inject+merge')     { n.times { list.inject({})           { |map, item| map.merge(item[:name] => item) } } }
  bm.report('inject+assign')    { n.times { list.inject({})           { |map, item| map[item[:name]] = item; map } } }
  bm.report('each')             { n.times { map = {}; list.each       { |item| map[item[:name]] = item } } }
end

# size = 10
#                        user     system      total        real
# each_with_object   0.020000   0.000000   0.020000 (  0.019710)
# inject+merge       0.140000   0.000000   0.140000 (  0.151981)
# inject+assign      0.020000   0.000000   0.020000 (  0.021939)
# each               0.020000   0.000000   0.020000 (  0.018951)

# size = 100
#                        user     system      total        real
# each_with_object   0.210000   0.000000   0.210000 (  0.205544)
# inject+merge      11.870000   0.190000  12.060000 ( 12.261768)
# inject+assign      0.200000   0.000000   0.200000 (  0.202474)
# each               0.180000   0.010000   0.190000 (  0.190451)