What Are The New Fold Expressions In C++ 17

C++17 is another big milestone in the history of C++, it comes with a lot of new features. In C++17, the fold expressions feature is a powerful feature that allows us to fold a parameter pack over a binary operator. Folding Expressions are very useful with variadic templates, and this feature makes template arguments more readable and concise. There are 4 different types of usage and in this post we will give syntax and simple examples about each of them.

What are the fold expressions that comes in C++ 17 features?

The fold expressions are established after the C++17 standard, they are used to fold (reduce) a parameter pack (fold_pack) over a binary operator (fold_op). The opening and closing parentheses are required in a fold expression.

In a folding expression there are 4 parameters,

• fold_pack is an expression that has parameter pack and no operator
• fold_op is a binary operator, one of the + – * / % ^ & | ~ = < > << >> += -= *= /= %= ^= &= |= <<= >>= == != <= >= && || , .* ->* operators
• fold_init is an initial expression at the beginning or at the end
• ... is an ellipses symbol that used for arguments

There are 4 different syntax in usage, now let’s see them in examples,

Is there a simple example about unary right fold expression?

Unary right fold expression syntax (since C++17),

here is an unary right fold expression example,

Is there a simple example about unary left fold expression?

Unary left fold expression syntax (since C++17).

here is an unary left fold expression example,

Is there a simple example about binary right fold expression?

Binary right fold expression syntax (since C++17).

here is a binary right fold expression example,

Is there a simple example about binary left fold expression?

Binary left fold expression syntax (since C++17).

here is a binary left fold expression example,

Is there a full example about fold expressions in C++ 17?

Here is a full example about fold expressions in C++17 that has 4 different types in usage.

and the output will be as follows:

For more details, please see this https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4295.html
and this https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0036r0.pdf

If you want to know more about about Variadic Templates, here are examples,

Learn What Is A Variadic Template in C++

See more

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