Extract state query method definition and quiet method redefinition warning.

activemodel/lib/active_model/state_machine.rb

@@ -31,6 +31,12 @@ def state_machine(name = nil, options = {}, &block)
         state_machines[name] ||= Machine.new(self, name)
         block ? state_machines[name].update(options, &block) : state_machines[name]
       end
+
+      def define_state_query_method(state_name)
+        name = "#{state_name}?"
+        undef_method(name) if method_defined?(name)
+        class_eval "def #{name}; current_state.to_s == %(#{state_name}) end"
+      end
     end
 
     def current_state(name = nil, new_state = nil, persist = false)

activemodel/lib/active_model/state_machine/state.rb

@@ -5,11 +5,8 @@ class State
 
       def initialize(name, options = {})
         @name = name
-        machine = options.delete(:machine)
-        if machine
-          machine.klass.send(:define_method, "#{name}?") do
-            current_state.to_s == name.to_s
-          end
+        if machine = options.delete(:machine)
+          machine.klass.define_state_query_method(name)
         end
         update(options)
       end