Mistake 18: replacing a variable-length parameter list with a vector adds storage and loop management where a variadic template can accept arguments directly. section 4.1
Define a base case for one argument, then a recursive case containing the remaining parameter pack. The compiler repeatedly expands the calls until only the base case remains. C++17 fold expressions can condense the recursive implementation. section 4.1
Listing 4.1 Using a vector to implement a variadic parameter list
template <typename T>
T sum(T initial, const std::vector<T>& vals) { #1
T sum = initial;
for (int i = 0; i < vals.size(); ++i)
sum += vals[i];
return sum;
}
int main() {
std::vector<int> intvalues; #2
for (int i = 1; i < 10; ++i) #3
intvalues.push_back(i);
std::cout << sum(0, intvalues) << '\n'; #4
std::vector<double> doublevalues;
for (int i = 1; i < 4; ++i)
doublevalues.push_back(i);
std::cout << sum(5.0, doublevalues) << '\n';
return 0;
}
Compare the vector-based sum with the templatized variadic version and its C++17 fold-expression alternative. section 4.1
