Enhancing Object Initializers with the “From-the-End” Index Operator

In the dynamic landscape of programming languages, even seemingly minor enhancements can significantly impact code readability and efficiency.

One such enhancement introduced in C# 13 is the “from-the-end” index operator (^). It allows developers to access elements from the end of an array or collection, simplifying array initialization within object initializers.

Compatibility

Keep in mind that this feature is available starting from C# 13. If you’re working with earlier versions, you’ll need to stick to indexing from the front.

Understanding the “From-the-End” Index Operator

The ^ operator, also known as the “from-the-end” index operator, provides a convenient way to access elements from the end of an array or collection. It is particularly useful when initializing arrays within object initializers.

Object Initializers in C

Before diving into the new feature, let’s revisit object initializers. In C#, object initializers allow you to create an instance of an object and set its properties or fields in a single statement. This eliminates the need for invoking constructors followed by multiple assignment statements.

Consider a simple example using a Cat class:

public class Cat
{
    public int Age { get; set; }
    public string? Name { get; set; }
}

// Using object initializer
Cat cat = new Cat { Age = 10, Name = "Fluffy" };

In the above code, we create a Cat instance and set its Age and Name properties using an object initializer.

Leveraging the “From-the-End” Index Operator

Now let’s explore the exciting part — the use of the ^ operator within an object initializer. Imagine we have a Matrix class with an indexer that allows us to set values at specific positions:

public class Matrix
{
    private double[,] storage = new double[3, 3];
    public double this[int row, int column]
    {
        get => storage[row, column];
        set => storage[row, column] = value;
    }
}

Suppose we want to initialize an identity matrix using the Matrix class. Traditionally, we’d index the elements from the front:

var identity = new Matrix
{
    [0, 0] = 1.0,
    [0, 1] = 0.0,
    [0, 2] = 0.0,
    // ... and so on
};

However, with the new feature, we can use the “from-the-end” index operator to make our code more concise:

var identity = new Matrix
{
    [^0, ^0] = 1.0,
    [^0, ^1] = 0.0,
    [^0, ^2] = 0.0,
    // ... and so on
};

By using ^0, we indicate the last element in each dimension. This not only improves readability but also aligns with our natural understanding of matrices.

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