Groovy def l = [1, 2, 3] as BlockingQueue

Question

If I write something like def l = [1, 2, 3] as Socket which is obviously nonsense, I get this:

org.codehaus.groovy.runtime.typehandling.GroovyCastE         


        

Answer 1

Using x as y is not casting, it's Coercion (see Section 8.7 of the Groovy Manual).

Coercion does not check type safety when casting.

Also, BlockingQueue is an interface. I'm not sure why you would cast an object as an interface.

Try running this:

import java.util.concurrent.LinkedBlockingQueue 
LinkedBlockingQueue l = [1, 2, 3] as LinkedBlockingQueue
println(l instanceof LinkedBlockingQueue)
println(l.class)
println(l.metaClass.methods*.name.sort().unique())
​

You get:

true
class java.util.concurrent.LinkedBlockingQueue
[add, addAll, clear, contains, containsAll, drainTo, element, equals, getClass, hashCode, isEmpty, iterator, notify, notifyAll, offer, peek, poll, put, remainingCapacity, remove, removeAll, retainAll, size, take, toArray, toString, wait]

You can't have an instance of an interface, so it had no idea what you asked it to do. For instance, try running new BlockingQueue(), you can't because you can't have an instance of an interface. This is why you cannot cast an Object to be an interface.