How C# 11 enabled ref fields inside ref struct types:

public ref struct CustomSpanReader<T>
{
    private ref T _current; // Ref field pointing directly into stack/heap memory
    private int _length;
    
    public CustomSpanReader(Span<T> span)
    {
        _current = ref MemoryMarshal.GetReference(span);
        _length = span.Length;
    }
}

Allows building custom enumerators, parsing streams, and windowed buffer scanners with direct pointer-like performance while maintaining 100% memory safety.

ref fields made it possible to write custom Span-like types in standard C# without dropping into unsafe pointer code.

A major feature for high-performance parser and network protocol library maintainers.