Virtual & Pure methods macros raises an error if concrete method exists

lib/virtual.rb

@@ -1,3 +1,4 @@
+require 'virtual/method_defined'
 require 'virtual/virtual_method'
 require 'virtual/pure_method'
 require 'virtual/protocol_method'

lib/virtual/method_defined.rb

@@ -0,0 +1,15 @@
+module Virtual
+  module MethodDefined
+    def self.call(target_class, method_name)
+      target_class.method_defined?(method_name, true) ||
+        target_class.private_method_defined?(method_name, true)
+    end
+
+    module SourceLocation
+      def self.get(target_class, method_name)
+        method = target_class.instance_method(method_name)
+        method.source_location.join(':')
+      end
+    end
+  end
+end

lib/virtual/pure_method.rb

@@ -3,6 +3,11 @@ module PureMethod
     Error = Class.new(RuntimeError)
 
     def self.define(target_class, method_name)
+      if MethodDefined.(target_class, method_name)
+        method_source_location = MethodDefined::SourceLocation.get(target_class, method_name)
+        raise Error, "Pure virtual (abstract) method #{method_name} of #{target_class.name} must not already be implemented (Source Location: #{method_source_location})"
+      end
+
       target_class.send(:define_method, method_name) do |*args|
         raise Error, "Pure virtual (abstract) method #{method_name} of #{self.class.name} must be implemented"
       end

lib/virtual/virtual_method.rb

@@ -6,6 +6,11 @@ def self.define(target_class, method_name, &blk)
       blk ||= proc do |*|
       end
 
+      if MethodDefined.(target_class, method_name)
+        method_source_location = MethodDefined::SourceLocation.get(target_class, method_name)
+        raise Error, "Virtual (abstract) method #{method_name} of #{target_class.name} must not already be implemented (Source Location: #{method_source_location})"
+      end
+
       target_class.send(:define_method, method_name, &blk)
     end
   end