many vs flat_map bench

many_vs_flat_map_bench.rb

# See:
#  - https://codon.com/refactoring-ruby-with-monads#multiple-results
#  - Rails PR: https://github.com/rails/rails/issues/37875 

require "benchmark_driver"

Benchmark.driver do |x|
  x.prelude %Q{
Blog     = Struct.new(:categories)
Category = Struct.new(:posts)
Post     = Struct.new(:comments)

blogs = [
  Blog.new([
    Category.new([
      Post.new(['I love cats', 'I love dogs']),
      Post.new(['I love mice', 'I love pigs'])
    ]),
    Category.new([
      Post.new(['I hate cats', 'I hate dogs']),
      Post.new(['I hate mice', 'I hate pigs'])
    ])
  ]),
  Blog.new([
    Category.new([
      Post.new(['Red is better than blue'])
    ]),
    Category.new([
      Post.new(['Blue is better than red'])
    ])
  ])
]

Many = Struct.new(:values) do
  def and_then(&block)
    Many.new(values.map(&block).flat_map(&:values))
  end

  def method_missing(*args, &block)
    and_then do |value|
      Many.new(value.public_send(*args, &block))
    end
  end
end
  }
  x.report "flat_map", %{ blogs.flat_map(&:categories).flat_map(&:posts).flat_map(&:comments) }
  x.report "many", %{ Many.new(blogs).categories.posts.comments.values }
end

__END__

Warming up --------------------------------------
            flat_map   904.475k i/s -    915.450k times in 1.012134s (1.11μs/i)
                many   184.317k i/s -    191.160k times in 1.037126s (5.43μs/i)
Calculating -------------------------------------
            flat_map   918.651k i/s -      2.713M times in 2.953708s (1.09μs/i)
                many   189.590k i/s -    552.951k times in 2.916557s (5.27μs/i)

Comparison:
            flat_map:    918650.5 i/s 
                many:    189590.3 i/s - 4.85x  slower