to_struct_2_example.rb

require "json"
require 'benchmark'
require 'bigdecimal/math'

class Hash
  def to_struct
    k = self.keys
    klass = k.map(&:to_s).sort_by {|word| word.downcase}.join.capitalize
    begin
      Kernel.const_get("Struct::" + klass).new(*self.values_at(*k))
    rescue NameError
      Struct.new(klass, *(k)).new(*self.values_at(*k))
    end
  end
end

# You have a hash that you have built in your app
sample_hash = {
  foo_key: "foo_val",
  bar_key: "bar_val",
  baz_key: "baz_val",
  foo1_key: "foo_val",
  bar1_key: "bar_val",
  baz1_key: "baz_val",
  foo2_key: "foo_val",
  bar2_key: "bar_val",
  baz2_key: "baz_val",
  foo3_key: "foo_val",
  bar3_key: "bar_val",
  baz3_key: "baz_val",
  foo4_key: "foo_val",
  bar4_key: "bar_val",
  baz4_key: "baz_val",
  foo5_key: "foo_val",
  bar5_key: "bar_val",
  baz5_key: "baz_val",
  foo6_key: "foo_val",
  bar6_key: "bar_val",
  baz6_key: "baz_val",
  foo7_key: "foo_val",
  bar7_key: "bar_val",
  baz7_key: "baz_val",
}

# Then you have JSON coming from some external api
json_response = "{\"qux_key\":\"qux_val\",\"quux_key\":\"quux_val\",\"corge_key\":\"corge_val\"}"
hash_with_unknown_keys = JSON.parse(json_response)

# Merge these two together
sample_hash.merge!(hash_with_unknown_keys)

iterations = 100_000

Benchmark.bm do |bm|
  bm.report "#to_struct" do
    iterations.times do
      # Would be super nice if I could convert this to a struct with a method
      # Somehow a bit faster than the explicit example below and much faster than open struct
      sample_struct = sample_hash.to_struct
      unless sample_struct.foo_key == "foo_val"
        raise "Wrong value"
      end
    end
  end

  bm.report "Struct" do
    iterations.times do
      sample_struct = Struct.new(*sample_hash.keys)
        .new(*sample_hash.values)
      unless sample_struct.foo_key == "foo_val"
        raise "Wrong value"
      end
    end
  end

  bm.report "OpenStruct" do
    iterations.times do
      sample_open_struct = OpenStruct.new(sample_hash)
      unless sample_open_struct.foo_key  == "foo_val"
        raise "Wrong value"
      end
    end
  end
end

#       user     system      total        real
# #to_struct  4.030000   0.010000   4.040000 (  4.072031)
#     Struct  6.870000   0.290000   7.160000 (  7.320459)
# OpenStruct 23.550000   0.210000  23.760000 ( 23.895187)