.Future!: ClassType
.Future!.
    result: (self: Ref Future!) -> Obj
    exception: (self: Ref Future!) -> Exception
    done: (self: Ref Future!) -> Bool
    cancelled: (self: Ref Future!) -> Bool
    set_result!: (self: RefMut Future!, result: Obj) => NoneType
    set_exception!: (self: RefMut Future!, exception: Exception) => NoneType
    cancel!: (self: RefMut Future!, msg := Str) => Bool

.isfuture: (obj: Obj) -> Bool