Kotlin Extension Methods


  • fun TypeName.extensionName(params, ...) { /* body */ } // Declaration
  • fun <T: Any> TypeNameWithGenerics<T>.extensionName(params, ...) { /* body */ } // Declaration with Generics
  • myObj.extensionName(args, ...) // invocation


Extensions are resolved statically. This means that the extension method to be used is determined by the reference-type of the variable you are accessing; it doesn't matter what the variable's type is at runtime, the same extension method will always be called. This is because declaring an extension method doesn't actually add a member to the receiver type.