How does one return from a groovy closure and stop its execution

closuresgroovyreturn

I would like to return from a closure, like one would if using a break statement in a loop.

For example:

largeListOfElements.each{ element->
    if(element == specificElement){
        // do some work          
        return // but this will only leave this iteration and start the next 
    }
}

In the above if statement I would like to stop iterating through the list and leave the closure to avoid unnecessary iterations.

I've seen a solution where an exception is thrown within the closure and caught outside, but I'm not too fond of that solution.

Are there any solutions to this, other than changing the code to avoid this kind of algorithm?

Best Answer

I think you want to use find instead of each (at least for the specified example). Closures don't directly support break.

Under the covers, groovy doesn't actually use a closure either for find, it uses a for loop.

Alternatively, you could write your own enhanced version of find/each iterator that takes a conditional test closure, and another closure to call if a match is found, having it break if a match is met.

Here's an example:

Object.metaClass.eachBreak = { ifClosure, workClosure ->
    for (Iterator iter = delegate.iterator(); iter.hasNext();) {
        def value = iter.next()
        if (ifClosure.call(value)) {
            workClosure.call(value)
            break
        }        
    }
}

def a = ["foo", "bar", "baz", "qux"]

a.eachBreak( { it.startsWith("b") } ) {
    println "working on $it"
}

// prints "working on bar"
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