Fold expressions

The C++ 17 standard added support for fold expressions to ease the generation of variadic functions. The Compiler does pattern matching and generates the code by inferring the intent of the programmer. The following code snippet demonstrates the idea:

//---------------- Folds.cpp
//--------------- Requires C++ 17 (-std=c++1z )
//--------------- http://en.cppreference.com/w/cpp/language/fold
#include <functional>
#include <iostream>

using namespace std;
template <typename... Ts>
auto AddFoldLeftUn(Ts... args) { return (... + args); }
template <typename... Ts>
auto AddFoldLeftBin(int n,Ts... args){ return (n + ... + args);}
template <typename... Ts>
auto AddFoldRightUn(Ts... args) { return (args + ...); }
template <typename... Ts>
auto AddFoldRightBin(int n,Ts... args) { return (args + ... + n); }
template <typename T,typename... Ts>
auto AddFoldRightBinPoly(T n,Ts... args) { return (args + ... + n); }
template <typename T,typename... Ts>
auto AddFoldLeftBinPoly(T n,Ts... args) { return (n + ... + args); }

int main() {
    auto a = AddFoldLeftUn(1,2,3,4);
    cout << a << endl;
    cout << AddFoldRightBin(a,4,5,6) << endl;
    //---------- Folds from Right
    //---------- should produce "Hello  World C++"
    auto b = AddFoldRightBinPoly("C++ "s,"Hello "s,"World "s );
    cout << b << endl;
    //---------- Folds (Reduce) from Left
    //---------- should produce "Hello World C++"
    auto c = AddFoldLeftBinPoly("Hello "s,"World "s,"C++ "s );
    cout << c << endl;
}

The expected output on the console is as follows

10
 25
 Hello World C++
 Hello World C++