CODEWITHSUNDEEP
c++templates
Maghoumi
Maghoumi

Reputation: 3388

Overload resolution based on template parameter

I'm unsure if what I want to do is possible in C++, so asking here.

I have a templated class MyClass that has an optional template argument idx. I have another non-templated class OtherClass. What I want to do is to do some sort of overload resolution based on idx:

Note that if T==SomeType the user of MyClass would provide idx. In other cases, no idx is needed. Also, the two different versions of OtherClass::otherMethod are guaranteed to take different input types. Seems to me that I somehow need to disable overload resolution for OtherClass::otherMethod<> when idx == -1 and enable it only if idx!= -1.

The code below outlines what I have:

template <typename T, int32_t idx=-1>
class MyClass
{
    OtherClass m_other;

    void myMethod(T arg)
    {
        // If idx == -1
        // m_other.otherMethod<idx>(arg);

        // else
        // m_other.otherMethod(arg);
    }
}

class OtherClass
{

    template<int32_t idx>
    void otherMethod(SomeType arg)
    {
        // Some operation that depends on idx
    }

    void otherMethod(YetAnotherType arg)
    {

    }
}

EDIT:
One obvious solution is to template void otherMethod(YetAnotherType arg) with some default (and unused) argument. I'm looking for solutions other than that.

EDIT2: (in response to comments)
I'm using C++11. A simple if doesn't always work, as demonstrated here. Thus, I need to know whether what I need to do is possible with compile-time constructs.

Upvotes: 0

Views: 68

Answers (1)

Igor Tandetnik
Igor Tandetnik

Reputation: 52621

Something along these lines, perhaps:

template <typename T, int32_t idx=-1>
class MyClass {
  OtherClass m_other;

  void myMethodHelper(T arg, std::true_type) {
       m_other.otherMethod<idx>(arg);
  }
  void myMethodHelper(T arg, std::false_type) {
       m_other.otherMethod(arg);
  }

public:
  void myMethod(T arg) {
    myMethodHelper(arg, std::integral_constant<bool, (idx >= 0)>{});
  }
};

Demo

Upvotes: 1

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