Syntax

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

Remarks

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.