CODEWITHSUNDEEP
c++c++11templatesc++14variadic-templates
Mustafa COKER
Mustafa COKER

Reputation: 5

std::initializer_list usage in variadic template function

I can't understand how below code snippet works. Especially std::initializer_list usage.

template<typename ... T>
auto sum(T ... t)
{
   typename std::common_type<T...>::type result{};
   std::initializer_list<int>{ (result += t, 0) ... };

   return result;
}

Upvotes: 0

Views: 131

Answers (1)

asmmo
asmmo

Reputation: 7100

template<typename ... T>
auto sum(T ... t)
{
   //getting the common type of the args in t and initialize a new var
   //called result using default constructor
   typename std::common_type<T...>::type result{};

  //(result += t, 0) ... this just sum the result and the next arg in the
  //parameter pack and then returns zero, hence the initializer_list will be filled 
  //only by zeros and at the end result will hold the sum of the args 
   std::initializer_list<int>{ (result += t, 0) ... };

   return result;
}

It's equivalent to

template<typename ... T>
auto sum(T ... t)
{
    return (t+...);
}

Upvotes: 3

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