Is there a way to "force" a sub-class to have a static function?

I know this is probably impossible but is there any way to force all sub-classes of a certain class to have a static method? Either to make them implement one (like in pure virtual functions) or have the compiler complain they don't have it?

Quote:

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Originally Posted by 6tr6tr

I know this is probably impossible but is there any way to force all sub-classes of a certain class to have a static method? Either to make them implement one (like in pure virtual functions) or have the compiler complain they don't have it?

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Don't define the method at all in the base class. Code won't compile if the particular class doesn't supply the method, right?

You can't have static virtual functions.

brewbuck, did you miss the static part?

Quote:

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Originally Posted by Daved

You can't have static virtual functions.

brewbuck, did you miss the static part?

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No, I didn't miss it. I didn't suggest making it virtual. I was envisioning something like:

Code:

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template <typename C>
void foo()
{
    C::someStaticMethod();
}

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Which of course will not compile if the method doesn't exist for class C. In other words, my answer boils down to "You don't have to do anything special," but as usual I'm clueless as to what 6r6tr is actually trying to do here...

For instance, if he's trying to invoke a static method through a base object pointer and have the dispatch be polymorphic, then my response would be "the method cannot be static"

hmm... but "method" means "virtual function" in C++, but that might not be what 6tr6tr intended to mean.

Quote:

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Originally Posted by laserlight

hmm... but "method" means "virtual function" in C++, but that might not be what 6tr6tr intended to mean.

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Yeah, I'm being sloppy with terminology. Given 6tr6tr's admitted Java background I interpreted it in that context.

So, 6tr, what are you actually trying to do? Because your question indicates that you're going about it all wrong - there is no sane use case for requiring a subclass to have a static function. (There is a use case for requiring that some class - usually a template parameter - has one, but that's different.)

Sorry, I was unclear. Brewbuck has what I want to do with the templated function. The problem is that while the base class that defines the templated function will not have the static function, the classes used with the templated function might have a base class "between" them and the template-function class that does. Example:

Code:

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class Base
{
public:
    template <typename T> a()
    {
          T::staticFunc();
    }
};

class Middle : public Base
{
public:
    static void staticFunc()
    {
          ...;
    }
};

class Derived : public Middle
{
public:
    //Person forgot to put static function in
};

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So it's basically the same issue as the every-derived-needs-the-method problem of things like cloning and the visitor pattern.

There's no way to ensure the presence of these functions. But some people say that in such hierarchies, only the leaf classes should be concrete (and thus provide the function) - in other words, they say that it is a design error that your Middle class provides staticFunc().