Quite often I deal with tree structures where each node can contains a set of children nodes. When is time to cycle through all the nodes, to execute some logic, you need to write a standard recursive function, an operation that is quite boring and repetitive. The question is, is it possible to write a LINQ function called Flatten() that permits you to flatten down a tree of arbitrary depth down to an IEnumerable<T>? The answer is yes.
It is amazing how simple is writing such a function with the yield return keyword. The code is based on an extension method that accepts an element of type T and a function that is capable to take an element of type T and return its childrens. Inside the body of the function I simply return the root as first, then I iterate on all childrens and for each one recursively call the Flatten function.
How easy. The code probably is not optimum for performance, but it is simple, and I always follow the rule of the three M, Measure Measure Measure, so I do not care for performance problems right now. Now I can write this simple test
To verify that the code really flatten down the tree. Thanks to Extension Method and yield keyword you can write a simple function that flatten down a hierarchy with fews lines of code.