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I was recently tasked with thinking about returning optional tracing information about the execution of a complex algorithm. It's the kind of data you need to analyse the inner workings - a bit like logging of intermediate results but being programmatically available to the caller and optional.
I only had rather bad ideas that involve too many changes to the core algorithm, like passing additional parameters all the way through. Also I couldn't find anything on the web.
Adding a parameter is not changing an algorithm.
An example: Your complex algorithm is Quicksort. Usual call:
Quicksort (array, size)
As the caller I want to know for some reason in which order you created partitions. So I declare
Class partition { int left; int right; int pivot; }
I change the prototype to
Quicksort (array, size, vector <partition> *partitions = nil)
You add code that adds information to the partitions vector if it is not nil. And I call your code, optionally passing a partitions vector, and if I do so I can then examine the results at runtime. That’s what you were asked to do.
If your algorithm works by creating an object describing the problem and then calling a method that solves the problem described, then the logging / feedback parameter can be stored as an instance variable and doesn’t need passing around.
