Extract Function seem like a trivially easy refactoring. But in many situations, it turns out to be rather more tricky. In the case above, I defined printDetails so it was nested inside printOwing. That way it was able to access all the variables defined in printOwing. But that’s not an option to me if I’m programming in a language that doesn’t allow nested functions. Then I’m faced, essentially, with the problem of extracting the function to the top level, which means I have to pay attention to any variables that exist only in the scope of the source function. These are the arguments to the
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