Advanced C# Tips: Use ‘in’ Parameter Modifier for Large Value Types

In C#, the in parameter modifier is relatively a recent addition. It added in C# 7.2. The main point of in keyword is to pass a large value type to a method without copying the entire structure. Value types in C# are typically passed by value. This means that the entire thing is duplicated and handed off to the method. This may not be a big deal for small value types like int or bool. However, for larger value types, it can be quite expensive in terms of performance because it takes time and memory to take care of these copies.

The in keyword plays an important role in enhancing performance when dealing with large value types. Value types (primarily structs) are normally passed to methods by value. This means that the entire data structure is copied every time whenever the method is called. The in keyword helps to optimize this by allowing you to pass a large value type to a method by reference. In other words, it creates a pointer to the original data. This operation is much like passing by reference using the ref keyword, but with one crucial difference: the in keyword ensures that the method cannot modify the value being passed. You can read it, but you can’t make changes to it. This read-only feature makes in an excellent choice since it ensures the integrity of the data. It also helps improving performance by avoiding the unnecessary copying of large structures.

Consider a high-performance application, such as a graphics renderer or a simulation tool. You will have a large and complex data structure entity like an image or a 3D model. These structures may contain hundreds or even thousands of fields, and you may need to perform numerous operations on them without changing the original data. By using the in keyword, you can pass these structures to your methods with the assurance that they will not be modified, and without the performance penalty of copying large amounts of data. Here’s a hypothetical example of how in might be used:

public struct HighResolutionImage
{
    // Imagine this contains a large amount of pixel data
}

public class ImageProcessor
{
    public void ApplyFilter(in HighResolutionImage image, ImageFilter filter)
    {
         // The filter is applied to the image, 
         // but the original image is not modified.
         // This prevents the need to create a copy of the image each
 	 // time a filter is applied.
    }
}

In the example ImageProcessor class above, the ApplyFilter method is designed to work with HighResolutionImage instances. Without the in keyword, each call to ApplyFilter would create a copy of the HighResolutionImage, which could be very inefficient due to its size. By using in, the method has a read-only reference to the image, allowing it to process the data without the cost of copying and without the risk of altering the original image data.

As a summary, the in keyword is a lovely tool for developers working with large value types, I repeat, value types. It ensures that performance isn’t lost by unnecessary data copying across the program. It also helps maintain data integrity by preventing methods from modifying the data they are given. If you understand and utilize the in keyword properly, you can write more efficient and reliable code, especially in performance-critical applications.

Suleyman Cabir Ataman, PhD

Sharing on social media: