Using ranges when implementing an algorithm

D code favors the use of ranges when implementing algorithms because ranges are a natural abstraction for operating on sequences of elements. We'll implement a function that takes a range and calculates the average of the values.

Getting ready

First, we need to sketch out our algorithm and determine what functions and types we'll need from the range. The algorithm should accept a range as generic as possible for element types that make sense for us, without sacrificing efficiency. Since our algorithm is taking an average value, the elements should be numeric. We'll also need to be able to iterate over each individual item. However, we don't need to know the length ahead of time (we can keep a count while calculating the sum); we don't need random access and we don't need to save our position. All we need to know is whether it is empty, the current item, and be able to advance the iteration. The result is we need an input range, nothing more. Other...