How to declare method reference in groovy?

Question

Im trying to use method reference in groovy. And I could not get it working.

The following is working in groovy.

Option2> list.stream().map(user -> user.getName()).collect(Collectors.toList())

What Im trying to achieve?

Option1> list.stream().map(User::getName).collect(Collectors.toList())

The above call is giving following error.

unexpected token: : @ line 33, column 14.
User::getName
1 error

Any suggestions how I can achieve?

Answer 1

The :: shortcut to create a lambda is only supported since Groovy 3.0. With said version your code there should work just fine.

Yet, what you want to do there has shortcuts already in Groovy for a very long time. You can use the spread operator *. and it will give you an ArrayList back. E.g. list*.name is the "groovy" way to write that.

The main difference here is, that this operation is eager. If you need the lazyness of the Java streams (e.g. because your example is simplified), then you can always use a Groovy closure instead of a lambda. There might be need for a cast, but Groovy usually figures this things out quite fine.

E.g.: list.stream().map{ it.name }.collect(Collectors.toList())