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December 3, 2009

Groovy Goodness: Implicit Method doCall in Closure

After reading Mixing dynamic and static code in Groovy I learned about the implicit method available in a closure: doCall(). This method corresponds to the arguments and body of the closure. If we invoke a closure with the call() or the unnamed () syntax the doCall() method is invoked. We can use this method to run the closure from within the closure.

def sizeList = { list, counter = 0 ->
    if (list.size() == 0) {
        counter
    } else {
        doCall(list.tail(), counter + 1)  // Call closure self.
    }
}

assert 5 == sizeList([1,2,3,4,5])