A fold expression performs a fold of a template parameter pack over a binary operator.
* An expression of the form (... op e) or (e op ...), where op is a fold-operator and e is an unexpanded parameter pack, are called unary folds.
* An expression of the form (e1 op ... op e2), where op are fold-operators, is called a binary fold. Either e1 or e2 is an unexpanded parameter pack, but not both.

template <typename... Args>
bool logicalAnd(Args... args) {
    // Binary folding.
    return (true && ... && args);
}
bool b = true;
bool& b2 = b;
logicalAnd(b, b2, true); // == true

template <typename... Args>
auto sum(Args... args) {
    // Unary folding.
    return (... + args);
}
sum(1.0, 2.0f, 3); // == 6.0