Let's say we have the following enum declaration (in Java):

@interface Person {
String[] friends();
}

In Java, curly braces may be omitted if a person has just one friend:

@Person(friends="Joe")
class Jane {}

In Groovy, this gives a compile error:
Annotation list attributes must use Groovy notation [el1, el2]

Of course @Person(friends=["Joe"]) still works, but it would be nice if Groovy also supported the abbreviated syntax.