overloaded_function.md

Meta type overloaded function (tkOverloadedFunction)

metapp supports overloaded function.
When registering callable using function registerCallable in MetaRepo or MetaClass, if more than one callables have same name, all callables of the same name are combine to an overload function automatically.
Class metapp::OverloadedFunction is used to create overloaded function, though usually you don't need to use the class directly, since MetaRepo and MetaClass will do it for you.

class OverloadedFunction
{
public:
  OverloadedFunction();
  const std::deque<Variant> & getCallableList() const;
  void addCallable(const Variant & callable);
};

The meta type for OverloadedFunction implements meta interface MetaCallable.
OverloadedFunction behaves as if it's a single function. When calling MetaCallable::invoke on an OverloadedFunction, it tries to find the best matched function which has the largest rank from MetaCallable::rankInvoke and invoke it. If no function matched, exception metapp::IllegalArgumentException is raised.

Note: when registering overload functions in MetaRepo or MetaClass, the functions are not necessary C++ overloaded function. The functions can be in different name, or in different type, such as one function is a free function, the other is std::function.
Any functions under the same name in MetaRepo or MetaClass are treated as overloaded function.

Now let's see how to use overload function in MetaRepo.

A free function.

std::string f1(int a)
{
  return std::to_string(a);
}

metapp::MetaRepo metaRepo;

Register the free function under name "func".

metaRepo.registerCallable("func", &f1);

Register std::function under the same name "func".

metaRepo.registerCallable("func", std::function<std::string (int, const std::string &)>(
  [](int a, const std::string & b) {
    return std::to_string(a) + b;
  }
));

Get the overload function.

const metapp::MetaItem & func = metaRepo.getCallable("func");

Now let's call the overload function.

// Invoke f1
ASSERT(metapp::callableInvoke(func, nullptr, 5).get<const std::string &>() == "5");
// Invoke std::function
ASSERT(metapp::callableInvoke(func, nullptr, 6, "good").get<const std::string &>() == "6good");