Types of Fold Expression

Fold expressions come in four types:

1. Unary Right Fold:

(pack op ...)

2. Unary Left Fold:

(... op pack)

3. Binary Right Fold:

(pack op ... op init)

4. Binary Left Fold:

(init op ... op pack)

In a binary fold expression, both operators op must be the same.

Fold expressions in C++17 are a powerful feature that allows you to reduce or “fold” a parameter pack over a binary operator. They were introduced to simplify code that operates on variadic templates and make it more concise and readable.