# UNDF: UNDF-2026-000000247
Fixes rails-0008: ActiveRecord Enum — value_method_names Array#include? inside pairs.each loop O(E²).

--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb

@@ DEFECT rails-0008: line 251-276

-        value_method_names = []                                          # Array — O(E) include?
+        value_method_names = Set.new                                     # FIX: Set for O(1) include?
         _enum_methods_module.module_eval do
           prefix = if prefix
             prefix == true ? "#{name}_" : "#{prefix}_"
           end

           suffix = if suffix
             suffix == true ? "_#{name}" : "_#{suffix}"
           end

           pairs = values.respond_to?(:each_pair) ? values.each_pair : values.each_with_index
           pairs.each do |label, value|
             enum_values[label] = value
             label = label.to_s

             value_method_name = "#{prefix}#{label}#{suffix}"
             value_method_names << value_method_name
             define_enum_methods(name, value_method_name, value, scopes, instance_methods)

             method_friendly_label = label.gsub(/[\W&&[:ascii:]]+/, "_")
             value_method_alias = "#{prefix}#{method_friendly_label}#{suffix}"

             if value_method_alias != value_method_name && !value_method_names.include?(value_method_alias)  # O(1) with Set
               value_method_names << value_method_alias
               define_enum_methods(name, value_method_alias, value, scopes, instance_methods)
             end
           end
         end
-        detect_negative_enum_conditions!(value_method_names) if scopes   # works with Set (responds to each)
+        detect_negative_enum_conditions!(value_method_names.to_a) if scopes  # convert back if Array needed

# BEFORE: value_method_names is Array; include? is O(E) called E times → O(E²)
# AFTER:  value_method_names is Set;   include? is O(1)             → O(E)
# Note: detect_negative_enum_conditions! only iterates — to_a needed if it checks index/[]
# Speedup: ~E× at E=1000 enum values