The main use of Unit, is that Unit is default return type for functions. Unit is the direct equivalent of Python None, however it is not as convenient in Kotlin to use Unit for all normal uses of None in python. However Python never enforces following rules for types. The above example saying ‘b’ is an int, then providing a default value of ‘None’ which is not an ‘int’ would be strictly speaking, breaking the rules. If a python program is actually declaring types (as with the parameter ‘a’ in the above example, then allowing None as an alternate value requires Union types, (e.g union of int and None as the type signature) but most code does not specify types, and Union types are reasonably concise if they are needed. # function ends with no return if it gets here, so will return NoneĪ variable can also be set to ‘None’ there is currently no value for that variable.įurther, a parameter can default to None, to indicate that no value was supplied.

Secondly, ‘None’ can be an alternative value to any expected type, the equivalent use pattern to the ‘null’ in Kotlin or Java. If the function has no return statement at all, then it will also return None. If a function in Python ends with the word ‘return’ with value to return, then the function will return a value of ‘None’. There are several uses of ‘None’.įirstly, ‘None’ is the default return value for any function that does specify a return type, the equivalent of this in Kotlin is the return type of Unit. In fact, python needs only this one way of saying ‘Nothing to see here’. The Python None is a singleton object of type NoneType. What is the actual difference in meaning for all of these?

Java has the keyword ‘ void‘ and the value ‘ null‘, kotlin has Unit, Nothing and null. Python has only one way of saying ‘there is nothing here’: None.

Nullable kotlin