Templates

• Situation: action performed on different data types
• Possible solution: write many functions taking arguments of many possible data types.
• Example: swapping the values of two variables
  

  void varSwap(int& a, int& b);
  void varSwap(double& a, double& b);
  ...

• Potentially an unlimited number of objects $\Rightarrow$ invalid approach
• Need for templates
  template<class TheClassName> returnType functionName(args);
  

  template<class T> void varSwap(T& a, T& b) {
  T tmp(b);
  b = a;
  a = tmp;
  }

Behaviour with predefined types:

int ia = 1;
int ib = 2;
varSwap(ia, ib);
cout « ia « ", " « ib « endl; // output: 2, 1

double da = 1.1;
double db = 2.2;
varSwap(da, db);
cout « da « ", " « db « endl; // output: 2.2, 1.1

Behaviour with user-defined types:

class MyClass {
public:
MyClass(std::string t) : myString(t) { }
$\tilde{\;}$ MyClass() { }
std::string getString(void) { return myString; }
void setString(std::string& t) { myString = t; }
private:
std::string myString;
};

MyClass ma("A");
MyClass mb("B");
varSwap(ma, mb);
cout « ma « ", " « mb « endl; // output: B, A