benchmarking selectively fetching keys from a ruby hash

bench.rb

require 'benchmark'

ATTRIBUTE_TYPES = {}.tap do |hash|
  struct = Struct.new(:searchable?)
  50.times do |i|
    searchable_val = [true, false].sample
    hash[i] = struct.new(searchable_val)
  end
end

n = 1_000_000

Benchmark.bm do |x|
  x.report("select{}.keys       ") do
    n.times do
      ATTRIBUTE_TYPES.select do |_, type|
        type.searchable?
      end.keys
    end
  end

  x.report("keys.select{}       ") do
    n.times do
      ATTRIBUTE_TYPES.keys.select do |key|
        ATTRIBUTE_TYPES[key].searchable?
      end
    end
  end

  x.report("keys.select!{}      ") do
    n.times do
      ATTRIBUTE_TYPES.keys.select! do |key|
        ATTRIBUTE_TYPES[key].searchable?
      end
    end
  end

  x.report("[].tap { x << key } ") do
    n.times do
      [].tap do |keys|
        ATTRIBUTE_TYPES.each do |key, type|
          keys << key if type.searchable?
        end
      end
    end
  end

  x.report("each_with_object([])") do
    n.times do
      ATTRIBUTE_TYPES.each_with_object([]) do |(key, type), keys|
        keys << key if type.searchable?
      end
    end
  end
end

Results

                     user     system      total        real
select{}.keys        15.060000   0.160000  15.220000 ( 15.360678)
keys.select{}        11.590000   0.140000  11.730000 ( 11.951267)
keys.select!{}       10.600000   0.070000  10.670000 ( 10.841434)
[].tap { x << key }  10.550000   0.050000  10.600000 ( 10.721592)
each_with_object([]) 14.880000   0.030000  14.910000 ( 15.078155)

In percentage terms (going off of the real column):

select{}.keys        |  0    %
keys.select{}        | 22.195%
keys.select!{}       | 29.420%
[].tap { x << key }  | 30.201%
each_with_object([]) |  1.839%