CODEWITHSUNDEEP
c++template-specialization
Shredderroy
Shredderroy

Reputation: 2920

Templated methods in a templated class

I would like to define a templated class

CTest<T>

in which one of the methods can return an object of type

CTest<U>

with T not necessarily equal to U, as follows:

template<typename T>
class CTest {
  // Properties
  private:
  T Prop_1;
  // Methods
  public:
  CTest::CTest (T);
  CTest::~CTest ();
  template<typename U>
  CTest<U> Method_1 (U);
};
template<typename T>
CTest<T>::CTest (T _Prop_1) {
  this->Prop_1 = _Prop_1;
}
template<typename T>
CTest<T>::~CTest () {
}
template<typename T, typename U>
CTest<U> CTest<T>::Method_1 (U _P) {
  CTest<U> Result (_P);
  return Result;
}

Actually, I've also tried defining Method_1 in the following way:

template<typename T>
template<typename U>
CTest<U> CTest<T>::Method_1 (U _P) {
  return CTest<U> (_P);
}

I tried to consume the class as follows:

int main () {
  CTest<int> Test (1);
  auto Test_2 = Test.Method_1<float> (2.0);
  return 0;
}

But I keep getting the compile-time error "unable to match function to an existing declaration." Thanks in advance for your help.

Upvotes: 1

Views: 689

Answers (1)

Dietmar K&#252;hl
Dietmar K&#252;hl

Reputation: 154045

It seems your primary problem are the constructor and destructor in the class definition: these should use extra qualification. Removing this junk causes the code to compiler for me with all compilers I have (gcc, clang, and EDG; for the latter I needed to remove auto Test 2 =). Here is the exact code I compiled:

template<typename T>
class CTest {
private:
    T Prop_1;
public:
    CTest (T);
    ~CTest ();
    template<typename U> CTest<U> Method_1 (U);
};
template<typename T>
CTest<T>::CTest (T _Prop_1) {
    this->Prop_1 = _Prop_1;
}
template<typename T>
CTest<T>::~CTest () {
}

template<typename T>
template<typename U>
CTest<U> CTest<T>::Method_1 (U _P) {
    return CTest<U> (_P);
}

int main () {
    CTest<int> Test (1);
    auto Test_2 = Test.Method_1<float> (2.0);
    return 0;
}

Upvotes: 2

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