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Groovy Goodness: More Efficient Tail Recursion With TailRecursive Annotation

See Gartner’s latest research on the application performance monitoring landscape and how APM suites are becoming more and more critical to the business, brought to you in partnership with AppDynamics.

Since Groovy 1.8 we can use the trampoline method for a closure to get better recursive behavior for tail recursion. All closure invocations are then invoked sequentially instead of stacked, so there is no StackOverFlowError. As from Groovy 2.3 we can use this for recursive methods as well with the @TailRecursive AST transformation. If we apply the annotation to our method with tail recursion the method invocations will be sequential and not stacked, like with the closure's trampoline method.

import groovy.transform.TailRecursive

@TailRecursive
long sizeOfList(list, counter = 0) {
    if (list.size() == 0) {
        counter
    } else {
       sizeOfList(list.tail(), counter + 1) 
    }
}

// Without @TailRecursive a StackOverFlowError
// is thrown.
assert sizeOfList(1..10000) == 10000

Code written with Groovy 2.3.

The Performance Zone is brought to you in partnership with AppDynamics.  See Gartner’s latest research on the application performance monitoring landscape and how APM suites are becoming more and more critical to the business.

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