How can I get a Span from a List while avoiding needless copies?

Question

I have a List containing some data. I would like to pass it to a function which accepts ReadOnlySpan.

List i         


        

Answer 1

In .Net 5.0, you can use CollectionsMarshal.AsSpan() (source, GitHub isue) to get the underlying array of a List as a Span.

Keep in mind that this is still unsafe: if the List reallocates the array, the Span previously returned by CollectionsMarshal.AsSpan won't reflect any further changes to the List. (Which is why the method is hidden in the System.Runtime.InteropServices.CollectionsMarshal class.)