This is a short blog post about a feature of Groovy closures I discovered a few days ago: Closure Composition.

With Closure Composition we can chain closure calls within a single closure.

Assume we have the following three closures:

def square = { it * it }
def plusOne = { it + 1 }
def half = { it / 2 }

Now we can combine those closures using the << or >> operators:

def c = half >> plusOne >> square

If we now call c() first half() will be called. The return value of half() will then be passed toplusOne(). At last square() will be called with the return value of plusOne().

println c(10) // (10 / 2 + 1)² -> 36

We can reverse the call order by using the << operator instead of >>

def c = half << plusOne << square

Now square() will be called before plusOne(). half() will be called last.

println c(10) // (10² + 1) / 2 -> 50.5