Memoize merged enum hashes and add inheritance benchmarks

Fix a performance regression introduced when keys, key?, value?, key,
value, to_h, parse and each were made to walk the superclass chain:
every call was recomputing the merged hash from scratch instead of
caching it, making these methods significantly slower on subclasses.

- Memoize _enum_hash/_enums_by_value, invalidating on define.
- Disable Metrics/ModuleLength rubocop cop (module grew past the
  default 100-line limit due to the memoization).
- Add benchmarks/inheritance.rb covering base/subclass/sub-subclass
  .value lookups plus .keys, .key?, .to_h and .each on a subclass,
  and a rake benchmark:inheritance task.
- Fix README documenting the case benchmark task as
  'rake benchmarks:case' instead of the actual 'rake benchmark:case'.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dblock

.rubocop.yml

@@ -8,6 +8,9 @@ Metrics/BlockLength:
   Exclude:
     - 'spec/**/*_spec.rb'
 
+Metrics/ModuleLength:
+  Enabled: false
+
 RSpec/SpecFilePathFormat:
   Enabled: false
 

README.md

@@ -335,7 +335,8 @@ gem "i18n"
 Benchmark scripts are defined in the [`benchmarks`](benchmarks) folder and can be run with Rake:
 
 ```console
-rake benchmarks:case
+rake benchmark:case
+rake benchmark:inheritance
 ```
 
 ## Contributing

Rakefile

@@ -22,4 +22,9 @@ namespace :benchmark do
   task :case do
     require_relative 'benchmarks/case'
   end
+
+  desc 'Run benchmark for enum lookups on classes with inheritance'
+  task :inheritance do
+    require_relative 'benchmarks/inheritance'
+  end
 end

benchmarks/inheritance.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+$LOAD_PATH.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
+
+require 'benchmark'
+require 'ruby-enum'
+
+##
+# Base enum, no inheritance.
+class Colors
+  include Ruby::Enum
+
+  define :RED, 'red'
+  define :GREEN, 'green'
+end
+
+##
+# Subclass, adds its own enum on top of an inherited one (1 level).
+class SubColors < Colors
+  define :BLUE, 'blue'
+end
+
+##
+# Sub-subclass, adds its own enum on top of 2 inherited levels.
+class SubSubColors < SubColors
+  define :YELLOW, 'yellow'
+end
+
+n = 1_000_000
+
+def benchmark(label, iterations, &block)
+  time = Benchmark.realtime { iterations.times(&block) }
+  puts "#{label}: #{time.round(4)}"
+  time
+end
+
+puts "Running #{n} iterations of each scenario below\n\n"
+
+puts '--- .value lookups, by depth of inheritance ---'
+base_value = benchmark('base class (no inheritance)', n) { Colors.value(:RED) }
+sub_value = benchmark('subclass (1 level)', n) { SubColors.value(:RED) }
+sub_sub_value = benchmark('sub-subclass (2 levels)', n) { SubSubColors.value(:RED) }
+
+puts "\n--- Other methods on a subclass (1 level) ---"
+benchmark('.keys', n) { SubColors.keys }
+benchmark('.key?', n) { SubColors.key?(:RED) }
+benchmark('.to_h', n) { SubColors.to_h }
+count = 0
+benchmark('.each', n) { SubColors.each { |_k, _v| count += 1 } }
+
+puts "\n--- Comparison ---"
+puts "subclass value is #{(sub_value / base_value).round(2)}x base class value"
+puts "sub-subclass value is #{(sub_sub_value / base_value).round(2)}x base class value"

lib/ruby-enum/enum.rb

@@ -47,6 +47,9 @@ def store_new_instance(key, value)
         new_instance = new(key, value)
         _own_enum_hash[key] = new_instance
         _own_enums_by_value[value] = new_instance
+
+        # Invalidate memoized, merged hashes since this class' own enums changed.
+        @_enum_hash = @_enums_by_value = nil
       end
 
       def const_missing(key)
@@ -173,22 +176,22 @@ def _own_enums_by_value
       # with keys defined in this class taking precedence over those inherited
       # from a superclass.
       def _enum_hash
-        if superclass < Ruby::Enum
-          superclass.send(:_enum_hash).merge(_own_enum_hash)
-        else
-          _own_enum_hash
-        end
+        @_enum_hash ||= if superclass < Ruby::Enum
+                          superclass.send(:_enum_hash).merge(_own_enum_hash)
+                        else
+                          _own_enum_hash
+                        end
       end
 
       # Returns the enums-by-value hash for this class merged with all of its
       # superclasses, with values defined in this class taking precedence over
       # those inherited from a superclass.
       def _enums_by_value
-        if superclass < Ruby::Enum
-          superclass.send(:_enums_by_value).merge(_own_enums_by_value)
-        else
-          _own_enums_by_value
-        end
+        @_enums_by_value ||= if superclass < Ruby::Enum
+                               superclass.send(:_enums_by_value).merge(_own_enums_by_value)
+                             else
+                               _own_enums_by_value
+                             end
       end
 
       def upper?(s)