CODEWITHSUNDEEP
c++templates
Hà Huy Long Hải
Hà Huy Long Hải

Reputation: 55

C++ Pass template argument through multiple functions

Consider these lines of code. When I try to compile the compiler will show errors like 'a' is not a member of 'DataType1'. I understand how the compiler treats these as errors but is there any way I could avoid this or another method that works?

struct DataType1 { public: int x; };
struct DataType2 { public: int a; };

template <class E>
bool job2(E* newData, const int i){
  int something = 2;  
  if (i == 1) newData->x = something;
  if (i == 2) newData->a = something;
}

template <class E>
bool job1(List<E>* dataBase){
  E* newData = new E;
  job2(newData, 1);
  dataBase->push_back(newData);
}

template <class E>
int main(){
  List<DataType1>* dataBase = new List<DataType>;
  job1(dataBase);
}

Upvotes: 0

Views: 207

Answers (1)

Timo
Timo

Reputation: 9825

If you have C++17 at hand you can write:

template <class E>
bool job2(E* newData){
  int something = 2;  
  if constexpr (std::is_same_v<E, DataType1>) 
     newData->x = something;
  else 
     newData->a = something;
}

and discard i alltogether (if you only used it to distinguish between types).

Othwerwise, what argues against simply overloading your function?

bool job2(DataType1* newData){
  commonOperation();
  newData->x = something;
}

bool job2(DataType2* newData){
  commonOperation();
  newData->a = something;
}

where commonOperation is everything the functions have in common.

Upvotes: 2

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