Statically extensible types allow a static type system to model the behavior of dynamic object model extension in dynamic runtime systems. Static types that model dynamically extended types can be extended using additional declarations in the same compilation. Declarations for a particular type can come from multiple independent sources which can have been defined at multiple points in time. Extension declarations can use the same syntax as the initial type declaration. Hence presence of one or more declarations for the same type in a compilation can indicate that the type has been extended. These features allow static type checking of dynamic plug-ins to be supported using statically extensible types. Declarations and extension declarations for a type can be merged together to create an extended type that enables different processing paths and dependencies.