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Groovy Goodness: More Efficient Tail Recursion With TailRecursive Annotation

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Groovy Goodness: More Efficient Tail Recursion With TailRecursive Annotation

· Java Zone
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What every Java engineer should know about microservices: Reactive Microservices Architecture.  Brought to you in partnership with Lightbend.

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.

Microservices for Java, explained. Revitalize your legacy systems (and your career) with Reactive Microservices Architecture, a free O'Reilly book. Brought to you in partnership with Lightbend.

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Published at DZone with permission of Hubert Klein Ikkink, DZone MVB. See the original article here.

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