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Generic Programming Templates in C++

- Examples

Discover how to use variadic templates to handle arbitrary arguments and perfect forwarding to preserve argument types when invoking constructors. This lesson provides practical examples that demonstrate compile-time size detection, recursive template specialization, and factory function patterns, helping you master advanced template techniques in C++.

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Example 1: Variadic Template

C++
// templateVariadicTemplates.cpp
#include <iostream>
template <typename... Args>
int printSize(Args... args){
  return sizeof ...(args);
}
template<int ...>
struct Mult;
template<>
struct Mult<>{
  static const int value= 1;
};
template<int i, int ... tail>
struct Mult<i, tail ...>{
  static const int value= i * Mult<tail ...>::value;
};
int main(){
  std::cout << std::endl;
  std::cout << "printSize(): " << printSize() << std::endl;
  std::cout << "printSize(template,2011,true): " << printSize("template",2011,true) << std::endl;
  std::cout << "printSize(1, 2.5, 4, 5, 10): " <<  printSize(1, 2.5, 4, 5, 10) << std::endl;
  std::cout << std::endl;
  std::cout << "Mult<10>::value: " << Mult<10>::value << std::endl;
  std::cout << "Mult<10,10,10>::value: " << Mult<10,10,10>::value << std::endl;
  std::cout << "Mult<1,2,3,4,5>::value: " << Mult<1,2,3,4,5>::value << std::endl;
  std::cout << std::endl;
}

Explanation

In the above example, we have used printSize function, which prints the number of elements (of any type) passed as arguments. It detects the number of elements on compile-time using the sizeof operator, and in case of an empty argument list, it returns 0.

There is a struct defined as Mult which takes arguments of integer type and return their product. If there is no argument passed, then it returns 1 which is the neutral element for multiplication. The result is stored in the value ...