I'm creating an API, and I want to overload a function for strip:

QString MyClass::strip();
QString MyClass::strip(QRegularExpression open);
QString MyClass::strip(QRegularExpression close);
QString MyClass::strip(QRegularExpression open, QRegularExpression close);

Obviously the second and third conflict.

What is the recommended style for C++ and Qt programmers to restructure this?

  • 1
    Default arguments?
    – Dawnkeeper
    Jan 13, 2016 at 13:01
  • 1
    @Dawnkeeper Does that solution work, when both parameters are not necessarily used? Think of it as "Dinner" and "Desert" ; Maybe I only want dinner, but not desert, or maybe I want desert, but not dinner. Maybe I want both! Maybe I want neither!
    – Anon
    Jan 13, 2016 at 13:11
  • 7
    You should give your functions different names, like stripOpen and stripClose.
    – gardenhead
    Jan 14, 2016 at 2:15
  • 1
    Just keep #4 and handle the case where open or close are null.
    – Florian F
    Jan 15, 2016 at 18:05
  • What gardenhead says. Don't be too smart about this. You may come up with a technical solution that works and feel good about it but you should first consider what it looks like at the client's end. Does it still read well? Is it obvious what your methods do when the user hits the dot and gets presented a list of methods? Jan 25, 2021 at 18:06

3 Answers 3


What about creating a class to hold your arguments? This class would contain both open and close parameters and either of them could be NULL. Then, there will be only one strip method with above class as argument and method will decide if it wants to use open/close if they are set.

  • Very interesting suggestion; I have never used this method. Can you give me an idea of what it would look like? Why a class, and not a struct?
    – Anon
    Jan 13, 2016 at 13:33
  • 3
    @Akiva Well, I don't think it matters if struct or class in this case.
    – Euphoric
    Jan 13, 2016 at 13:34
  • @Akiva C++ has class types defined with both struct and class keywords
    – Caleth
    Jan 25, 2021 at 17:31

There are many options, it's your tradeoff which to take:

Decision at runtime:

  1. Add a defaulted bool argument:

     QString MyClass::strip(QRegularExpression regex, bool close=false);
     // Mimic the two-regex-variants interface as good as possible
  2. Use scoped enum's and no default as a variant on 1 which is more descriptive:

     enum class option { open, close };
     QString MyClass::strip(QRegularExpression regex, option open_close);
  3. Use std::experimental::optional or something like that, maybe from boost.

  4. Find out that a specific regex does nothing, and document that as the no-op default.

Decision at compiletime:

  1. Use overloads replacing one argument with std::nullptr_t:

     QString MyClass::strip(std::nullptr_t open, QRegularExpression close);
     QString MyClass::strip(QRegularExpression open, std::nullptr_t close = {});
  2. Use tags to avoid any overhead:

     constexpr struct open_t {} open;
     constexpr struct close_t {} close;
     QString MyClass::strip(open_t, QRegularExpression regex);
     QString MyClass::strip(close_t, QRegularExpression regex);
     // Call it like this:
     object.strip(object.open, regex);
  3. Bite the bullet and name those functions differently:

     QString MyClass::strip_open(QRegularExpression regex);
     QString MyClass::strip_close(QRegularExpression regex);
  4. Consider whether making the open-regex and the close-regex different types makes sense. To be truthful, I doubt it here, but where appropriate that's the best option.

  • 2
    6. Don;t provide them Allow QString MyClass::strip(QRegularExpression open, QRegularExpression close); to take NULL parameters.
    – mattnz
    Jan 14, 2016 at 0:15
  • @mattnz Ohhh that is an interesting solution! Question is though; is there a naming scheme for the parameters that would indicate that null values are accepted? Perhaps Defaulting them both to "NULL" values?
    – Anon
    Jan 15, 2016 at 5:43
  • 1
    @Akiva: Elaborated on a way to achieve something like that. As an aside, you can combine using an optional type, replacing positional arguments with std::nullptr_t and using a "do nothing"-regex. Jan 15, 2016 at 13:31

I would suggest

QString MyClass::strip();
QString MyClass::strip(QRegularExpression regex, bool opening=false); 
QString MyClass::strip(QRegularExpression open, QRegularExpression close);

and perhaps

QString MyClass::strip_open(QRegularExpression regex);
QString MyClass::strip_close(QRegularExpression regex);

or replace the bool opening with e.g.

enum stripping_mode {Strip_Open, Strip_Close};;

or make even it a class enum

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