Fold Expressions vs Variadic Templates

Fold expressions, introduced in C++17, provide a more concise and expressive way to work with parameter packs compared to traditional variadic template techniques. Here are some advantages of using fold expressions:

Concise syntax: Fold expressions allow you to express common operations on parameter packs using a compact syntax. Traditional variadic template techniques often require recursive template instantiations and more verbose code.

Compare the following examples that calculate the sum of a parameter pack. Using traditional variadic templates:

1template <typename T>
2T SumValues(T Value) {
3  return Value;
4}
5
6template <typename T, typename... Types>
7T SumValues(T First, Types... Rest) {
8  return First + SumValues(Rest...);
9}

Using fold expressions:

1template <typename... Types>
2auto SumValues(Types... Args) {
3  return (... + Args);
4}

The fold expression version is much more concise and readable.

Improved readability: Fold expressions make the intent of the code more clear by directly expressing the operation being performed on the parameter pack. This improves code readability and maintainability.

Reduced boilerplate: With fold expressions, you don't need to write separate base cases and recursive cases for variadic templates. The fold expression handles both cases implicitly, reducing the amount of boilerplate code required.

Support for empty parameter packs: Fold expressions, particularly binary folds, provide built-in support for handling empty parameter packs. Traditional variadic templates often require explicit handling of empty parameter packs using specializations or if constexpr statements.

Flexibility with different operators: Fold expressions allow you to easily switch between different operators by simply changing the operator in the fold expression. Traditional variadic templates may require more changes to the code structure when switching operators.

However, it's worth noting that fold expressions are not a complete replacement for all variadic template techniques. There may be cases where the traditional techniques are still necessary or more suitable, such as when you need more fine-grained control over the recursion or when the operation cannot be expressed using a fold expression.

Overall, fold expressions provide a more concise and expressive way to work with parameter packs in many common scenarios, improving code readability and reducing boilerplate compared to traditional variadic template techniques.