Understanding the CLR constraints on ref struct types (like Span<T> and ReadOnlySpan<T>):

Because ref struct instances contain interior pointers directly into stack memory, the CLR guarantees they never escape to the managed heap where they could outlive their stack frames.

Forbidden in C#:

• Cannot be boxed (object o = mySpan; // Compiler Error)
• Cannot be a field of a normal class or struct
• Cannot be used in async methods across await boundaries (because async state machines are lifted to the heap upon suspension!)
• Cannot be captured in lambda closures.

In .NET, use Memory<T> / ReadOnlyMemory<T> when buffer references need to cross async/await boundaries safely!

Memory<T> is a regular struct that wraps an array or MemoryManager, so it is completely safe to store in classes or await in async methods.

Clear architectural breakdown of Span vs Memory lifetime boundaries.