Скачать или смотреть How to Effectively Use Variadic Templates in C+ + : Calling Functions for Each Type in a Typelist

Discover how to utilize `variadic templates` in C+ + to create functions that can operate on every type within a typelist. Learn step-by-step solutions in this comprehensive guide.
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Understanding Variadic Templates in C+ +

Variadic templates in C+ + are a powerful feature that allows us to define templates that can accept an arbitrary number of types as parameters. This can be particularly useful when you have a list of various types and you want to perform operations on each of these types without having to manually specify each one.

The Problem

Consider a typelist defined as follows:

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You also have a function template, foo(), which is designed to operate on a single type:

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Your goal is to call foo() for each type defined in my_list: int, double, bool, and float. Manually invoking the function for each type looks like this:

[[See Video to Reveal this Text or Code Snippet]]

However, this method can be cumbersome, especially when there are many types involved. You might be wondering if there’s a more elegant solution available.

The Solution

There are two effective approaches to solve this problem: one using fold expressions (available in C+ + 17) and one using classic template recursion.

Using Fold Expressions (C+ + 17 and newer)

If you have access to C+ + 17, you can utilize fold expressions, which make this process straightforward. Here’s how it can be done:

[[See Video to Reveal this Text or Code Snippet]]

How it works:

The foo_foreach function takes a typelist and uses a fold expression to invoke foo<Types>() for each type in the typelist.

The syntax (foo<Types>(), ...) ensures that foo is called for each type consecutively.

Using Template Recursion (C+ + 11 and later)

If you are using an older version of C+ + , you can achieve the same effect through template recursion. Here’s the classic approach:

[[See Video to Reveal this Text or Code Snippet]]

How it works:

The first foo_foreach function is a base case for an empty typelist.

The second foo_foreach function takes the head of the typelist (the first type) and calls foo with it, then recursively calls itself with the tail of the typelist (the remaining types).

Conclusion

By using either fold expressions or template recursion, you can create a neat and efficient way to operate on each type within a typelist in C+ + . This not only streamlines your code but also enhances its readability and maintainability. Experiment with these techniques in your C+ + projects to see the benefits firsthand!