Groovy not in collection

I think there is no not in pretty syntax, unfortunately. But you can use a helper variable to make it more readable:

def isMagicChar = ch in ['a', 'b', 'c']
if (!isMagicChar) ...

Or, in this case, you may use a regex :)

if (ch !=~ /[abc]/) ...

You can add new functions:

Object.metaClass.notIn = { Object collection ->
    !(delegate in collection)
}


assert "2".notIn(['1', '2q', '3'])
assert !"2".notIn(['1', '2', '3'])

assert 2.notIn([1, 3])
assert !2.notIn([1, 2, 3])

assert 2.notIn([1: 'a', 3: 'b'])
assert !2.notIn([1: 'a', 2: 'b'])

Another way to write it is with contains, e.g.

if (!['a', 'b', 'c'].contains('b'))

It saves the extra level of parentheses at the cost of replacing the operator with a method call.