C# 13 has introduced significant enhancements to ref structs, a stack-allocated value type that offers faster access and reduced memory footprint compared to regular structs. These improvements make ref structs an attractive choice for high-performance applications where resource consumption is critical.

In contrast to regular structs, ref structs cannot be boxed or unboxed, and their instances remain on the stack throughout their lifecycle. This characteristic makes them ideal for applications where memory allocation and deallocation in the stack are crucial. The ref struct keyword was first introduced in C# 7.2, but C# 13 extends their support in a more useful way, allowing local variables of the ref or ref struct type to be used in iterator and asynchronous methods.

The benefits of using ref structs are twofold: enhanced performance and deterministic lifetime. Because ref structs reside on the stack only, instances are allocated and deallocated much faster than instances of classes that reside on the managed heap. This eliminates garbage collection overhead, enabling faster data access. Additionally, the deterministic lifetime of ref structs ensures that instances are automatically deallocated from stack memory when they are no longer required, making them suitable for creating temporary objects.

To demonstrate the performance benefits of ref structs, consider a code example that creates a ref struct with a Span in C#. The parameter of type Span in the constructor of the ref struct is assigned to the private Span instance of the class. Because a ref struct instance doesn't require any heap allocation or boxing overhead when assigned to another object, memory overheads are reduced, and data access is accelerated.

While C# 13 has removed some longstanding limitations of ref structs, such as their use in iterators and asynchronous methods, there are still key limitations to keep in mind. For instance, an instance of type ref struct cannot be an element of an array, boxed to either System.Object or System.ValueType, or used as a generic argument when calling methods. Furthermore, a ref struct must implement all members of an interface it implements, even if the members of the interface have been implemented by default.

Another significant benefit of ref structs is their ability to be used with pointers in a safe context. This makes them a great choice in applications where stack-only allocation and high performance are essential. However, developers should exercise caution when using ref structs, as overusing them in recursive methods with low stack memory can lead to performance issues.

In conclusion, C# 13's enhanced ref structs offer a powerful tool for developers seeking to optimize their applications' performance and resource consumption. By understanding the benefits and limitations of ref structs, developers can harness their potential to create high-performance applications that meet the demands of modern computing.