What are ref structs and why cannot they live on the heap?
PICTURE THIS: STACK VS QUEUE
Simple meaning
ref struct types like Span can only live on the stack so they can safely point at stack memory.
WHY — C# instead of guessing?
Why interviewers care about C#:
who only read docs from people who shipped.
and tied to .NET work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1ref struct types like
Span can only live on the stack so they can safely point at stack memory.
- 2Why it exists
That restriction stops lifetime bugs.
- 3It also blocks async
locals and boxing.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
ref struct types like Span can only live on the stack so they can safely point at stack memory. That restriction stops lifetime bugs.