Can I extend an enum with additional values?

Question

If I have an enum with a set of values, is there a way I could create a second enum with the same variants plus some more?

// From this enum Base {     Alpha,     Beta(usize), }  // To this, but without copy & paste enum Extended {     Alpha,     Beta(usize),     Gamma, } 

Answer 1

An enum can't be directly extended, but you use the same composition trick one would use with structs (that is, with a struct, one would have a field storing an instance of the 'parent').

enum Base {     Alpha,     Beta(usize), }  enum Extended {     Base(Base),     Gamma } 

If you wish to handle each case individually, this is then used like

match some_extended {     Base(Alpha) => ...,     Base(Beta(x)) => ...,     Gamma => ... } 

but you can also share/re-use code from the "parent"

match some_extended {     Base(base) => base.do_something(),     Gamma => ..., }