Fix NoMethodError on enum methods when subclass defines no enums of its own

CHANGELOG.md

@@ -1,5 +1,6 @@
 ### 1.2.0 (Next)
 
+* [#49](https://github.com/dblock/ruby-enum/issues/49): Fixed `NoMethodError` on `keys`, `values`, `key?`, `value?`, `key`, `value`, `to_h`, `parse` and `each` when a subclass defines no enums of its own - [@dblock](https://github.com/dblock).
 * Your contribution here.
 
 ### 1.1.0 (2026/6/20)

lib/ruby-enum/enum.rb

@@ -31,9 +31,6 @@ module ClassMethods
       # [key] Enumerator key.
       # [value] Enumerator value.
       def define(key, value = key)
-        @_enum_hash ||= {}
-        @_enums_by_value ||= {}
-
         validate_key!(key)
         validate_value!(value)
 
@@ -48,8 +45,8 @@ def define(key, value = key)
 
       def store_new_instance(key, value)
         new_instance = new(key, value)
-        @_enum_hash[key] = new_instance
-        @_enums_by_value[value] = new_instance
+        _enum_hash[key] = new_instance
+        _enums_by_value[value] = new_instance
       end
 
       def const_missing(key)
@@ -59,7 +56,7 @@ def const_missing(key)
       # Iterate over all enumerated values.
       # Required for Enumerable mixin
       def each(&block)
-        @_enum_hash.each(&block)
+        _enum_hash.each(&block)
       end
 
       # Attempt to parse an enum key and return the
@@ -84,7 +81,7 @@ def parse(k)
       #
       # Returns true if the key exists, false otherwise.
       def key?(k)
-        @_enum_hash.key?(k)
+        _enum_hash.key?(k)
       end
 
       # Gets the string value for the specified key.
@@ -94,7 +91,7 @@ def key?(k)
       #
       # Returns the corresponding enum instance or nil.
       def value(k)
-        enum = @_enum_hash[k]
+        enum = _enum_hash[k]
         enum&.value
       end
 
@@ -105,7 +102,7 @@ def value(k)
       #
       # Returns true if the value exists, false otherwise.
       def value?(v)
-        @_enums_by_value.key?(v)
+        _enums_by_value.key?(v)
       end
 
       # Gets the key symbol for the specified value.
@@ -115,18 +112,18 @@ def value?(v)
       #
       # Returns the corresponding key symbol or nil.
       def key(v)
-        enum = @_enums_by_value[v]
+        enum = _enums_by_value[v]
         enum&.key
       end
 
       # Returns all enum keys.
       def keys
-        @_enum_hash.values.map(&:key)
+        _enum_hash.values.map(&:key)
       end
 
       # Returns all enum values.
       def values
-        result = @_enum_hash.values.map(&:value)
+        result = _enum_hash.values.map(&:value)
 
         if superclass < Ruby::Enum
           superclass.values + result
@@ -138,37 +135,51 @@ def values
       # Iterate over all enumerated values.
       # Required for Enumerable mixin
       def each_value(&_block)
-        @_enum_hash.each_value do |v|
+        _enum_hash.each_value do |v|
           yield v.value
         end
       end
 
       # Iterate over all enumerated keys.
       # Required for Enumerable mixin
       def each_key(&_block)
-        @_enum_hash.each_value do |v|
+        _enum_hash.each_value do |v|
           yield v.key
         end
       end
 
       def to_h
-        @_enum_hash.transform_values(&:value)
+        _enum_hash.transform_values(&:value)
       end
 
       private
 
+      # Returns this class' own enum hash, defaulting to an empty hash.
+      #
+      # A subclass that does not `define` any of its own enums does not have
+      # its `@_enum_hash` instance variable set, since it's only initialized
+      # in `define` and in the `included` hook.
+      def _enum_hash
+        @_enum_hash ||= {}
+      end
+
+      # Returns this class' own enums-by-value hash, defaulting to an empty hash.
+      def _enums_by_value
+        @_enums_by_value ||= {}
+      end
+
       def upper?(s)
         !/[[:upper:]]/.match(s).nil?
       end
 
       def validate_key!(key)
-        return unless @_enum_hash.key?(key)
+        return unless _enum_hash.key?(key)
 
         raise Ruby::Enum::Errors::DuplicateKeyError, name: name, key: key
       end
 
       def validate_value!(value)
-        return unless @_enums_by_value.key?(value)
+        return unless _enums_by_value.key?(value)
 
         raise Ruby::Enum::Errors::DuplicateValueError, name: name, value: value
       end

spec/ruby-enum/enum_spec.rb

@@ -24,6 +24,9 @@ class OtherSecondSubclass < FirstSubclass
     define :MAGENTA, 'magenta'
   end
 
+  class SubclassWithNoOwnDefines < Colors
+  end
+
   it 'returns an enum value' do
     expect(Colors::RED).to eq 'red'
     expect(Colors::GREEN).to eq 'green'
@@ -182,6 +185,12 @@ class OtherSecondSubclass < FirstSubclass
         expect(OtherSecondSubclass.values).to eq(%w[red green orange magenta])
       end
     end
+
+    context 'when a subclass defines no enums of its own' do
+      it 'returns the values from the parent class' do
+        expect(SubclassWithNoOwnDefines.values).to eq(%w[red green])
+      end
+    end
   end
 
   describe '#to_h' do
@@ -334,6 +343,28 @@ class EmptyEnums
         expect(FirstSubclass.values).to eq(%w[red green orange])
       end
     end
+
+    context 'when a subclass defines no enums of its own (issue #49)' do
+      it 'inherits the parent class enums via constants' do
+        expect(SubclassWithNoOwnDefines::RED).to eq 'red'
+        expect(SubclassWithNoOwnDefines::GREEN).to eq 'green'
+      end
+
+      it 'inherits the parent class values' do
+        expect(SubclassWithNoOwnDefines.values).to eq(%w[red green])
+      end
+
+      it 'does not raise when calling keys, key?, value?, key, value, to_h, parse or each' do
+        expect(SubclassWithNoOwnDefines.keys).to eq([])
+        expect(SubclassWithNoOwnDefines.key?(:RED)).to be false
+        expect(SubclassWithNoOwnDefines.value?('red')).to be false
+        expect(SubclassWithNoOwnDefines.key('red')).to be_nil
+        expect(SubclassWithNoOwnDefines.value(:RED)).to be_nil
+        expect(SubclassWithNoOwnDefines.to_h).to eq({})
+        expect(SubclassWithNoOwnDefines.parse('red')).to be_nil
+        expect(SubclassWithNoOwnDefines.each.to_a).to eq([])
+      end
+    end
   end
 
   describe 'default value' do