json_serialization_benchmark.cr

require "benchmark"
require "json"

class MenuItem

  def self.all
    h =  {
        "name": "Serdar",
        "age": 27,
        "email": "[email protected]",
        "skills": ["ruby", "rails", "crystal", "kemal"]
      }
    array = [] of (typeof(h))
    1000.times { array << h }
    array
  end

end

Benchmark.ips do |x|
  x.report "Mapping" do
    MenuItem.all.map do |mi|
      {
        "name": mi["name"],
        "age": mi["age"],
        "email": mi["email"],
        "skills": mi["skills"]
      }
    end.to_json
  end
  
  x.report "IO" do
    String.build do |io|
      MenuItem.all.each do |mi|
        io.json_object do |object|
          object.field "name", mi["name"]
          object.field "age", mi["age"]
          object.field "email", mi["email"]
          object.field "skills" do
            io.json_array do |array|
              (mi["skills"] as Array).each { |item| array << item }
            end
          end
        end
      end
    end
  end
end

crystal build --release json_serialization_benchmark.cr -o benchmark
./benchmark

Results

Mapping 893.39  (± 3.71%)  2.05× slower
     IO   1.83k (± 2.43%)       fastest