Mathematically, the purpose of a function is to return an output. However, in a programming context functions often have side effects. It is even common to call functions for the side effects alone. The classic example is print(x), which has a useful side effect and no output.

It seems to me that we can taxonomize functions into five classes based on human expectations about their outputs and side effects:

1. Functions with no side effects, where the output is most interesting
2. Functions with side effects, but the output is most interesting
   • Technically, all functions are like this, because running things on the computer always has side effects like using up CPU and RAM.
3. Functions with an output, but the side effect is more interesting than the output
   • Example: request(url, type="POST") - the output is only a detail if we care to check whether the request succeeded, which may even be irrelevant in some cases
4. Functions with no output, executed for their side effects
5. Functions with no output or side effect to speak of (usually created for testing or as placeholders)

Is there a terminology for these classes?

posted 9 months ago

CC BY-SA 4.0

9mo ago

matthewsnyder‭

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