How to Initialize std::array Members in a Constructor in C++

Learn how to efficiently initialize `std::array` members in C++ constructors using modern techniques to simplify your code and maintain performance.
---

Visit these links for original content and any more details, such as alternate solutions, comments, revision history etc. For example, the original title of the Question was: Initilise std::array member in constructor?

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Initialize std::array Members in a Constructor in C++

When working with C++, you might find yourself needing to initialize a std::array member within a class constructor. While straightforward, this task can become cumbersome, especially when you're dealing with template parameters that affect the array's dimensions. In this guide, we will explore a more efficient way to handle this initialization while keeping your code neat and easy to understand.

The Problem

Suppose we have a class that includes a std::array member. You may want to initialize it within the constructor, while also ensuring the dimensions are known at compile-time. Here's an example of what you might start with:

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

While this is okay, it can lead to a cluttered codebase, as you'll need to carry template parameters along with you in every function. Ideally, there should be a more straightforward way to manage the initialization and avoid dynamic memory allocation, without compromising the advantages of std::array.

The Solution

Using Class Template Argument Deduction (CTAD)

A modern approach introduced in C++20 is to utilize Class Template Argument Deduction (CTAD). To make this work effectively, first, we need to define a structure that captures the dimensions.

Step 1: Define a Dimensions Structure

You can define a class, dims, that holds the width and height as compile-time constants:

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

This structure prepares the ground for passing dimensions easily.

Step 2: Modify Your Class to Use Dims

Now, integrate this dims in your main class:

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

Step 3: Creating an Instance

Now that you have your class set up, you can create an object quite simply using CTAD:

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

This allows C++ to deduce the template parameters automatically from your constructor parameters.

Special Notes for C++17 Users

If you're still using C++17, you'll need a small tweak in your class definition to implement CTAD:

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

This directive instructs the compiler on how to deduce the template parameters based on the constructor argument.

Conclusion

Initializing a std::array within a constructor can be straightforward with the right techniques. By utilizing the dims structure and modern class template argument deduction, you can streamline your code and make it more maintainable. This approach not only enhances readability but also keeps all your memory allocation static, leveraging the benefits of std::array.

So the next time you're faced with initializing an array within a constructor, remember to use these C++20 features to create cleaner and more efficient code!