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When I have a function that might, or might not receive a certain parameter, is it better to overload the function, or to add optional args?

If each one has it's ups and downs - when would I use each?

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From the optimization perspective having optional parameters is a better option. –  Maneet Puri Jun 14 '12 at 10:58
    

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If the language supports them properly (e.g. type-safety, if applicable), I would prefer optional arguments for the following reasons:

  • They convey your intent better so noone suspects that your function overload will do something different (which it probably shouldn't anyway).
  • Less code to maintain, even if the function overload only delegates to the more comprehensive one. If you want to rename the function later, you have at least 3 places to do it (two definitions + one call).
  • The compiler (if any) might generate smaller binaries.
  • Optional arguments scale better, at least in some languages. What if you want to have 3 optional arguments with the ability to mix and match? For full flexibility, you'd need 6 overloads to do that.
  • If it's an object method, multiple overloads will greatly hinder the implementation of overrides in subclasses.
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Assuming a constructor kind of situation: I often choose a fluent builder pattern to prevent situations with many options.

Eg.Ordering.natural().onResultOf(function).reverse().compound(Ordering.natural().onResultOf(function2)) is an example of calling a fluent builder interface implemented in Guava.

Of course you now need a separate object to hold the state of your builder, but you reduce overall complexity by separating behavior of constructing from behavior of the constructed.

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