In object-oriented computer programming, an extension method is a method added to an object after the original object was compiled. The modified object is often a class, a prototype or a type. Extension methods are features of some object-oriented programming languages. There is no syntactic difference between calling an extension method and calling a method declared in the type definition. Not all languages implement extension methods in an equally safe manner, however. For instance, languages such as C#, Java (via Manifold or Lombok), and Kotlin don't alter the extended class in any way, because doing so may break class hierarchies and interfere with virtual method dispatching. This is why these languages strictly implement extension methods statically and use static dispatching to invoke them. Support in programming languages Extension methods are features of numerous languages including C#, Java via Manifold or Lombok, Gosu, JavaScript, Oxygene, Ruby, Smalltalk, Kotlin, Dart, Visual Basic.NET and Xojo. In dynamic languages like Python, the concept of an extension method is unnecessary because classes can be extended without any special syntax (an approach known as "monkey-patching", employed in libraries such as gevent). In VB.NET and Oxygene, they are recognized by the presence of the "extension" keyword or attribute. In Xojo the "Extends" keyword is used with global methods. In C# they're implemented as static methods in static classes, with the first argument being of extended class and preceded by "this" keyword. In Java you add extension methods via Manifold, a jar file you add to your project's classpath. Similar to C# a Java extension method is declared static in an @Extension class where the first argument has the same type as the extended class and is annotated with @This. In Smalltalk, any code can add a method to any class at any time, by sending a method creation message (such as methodsFor:) to the class the user wants to extend. The Smalltalk method category is conventionally named after the package that provides the extension, surrounded by asterisks. For example, when Etoys application code extends classes in the core library, the added methods are put in the *etoys* category. In Ruby, like Smalltalk, there is no special language feature for extension, as Ruby allows classes to be re-opened at any time with the class keyword, in this case, to add new methods. The Ruby community often describes an extension method as a kind of monkey patch. There is