Unsafe.As vs Unsafe.BitCast

[colejohnson66]

What's the difference between Unsafe.As and Unsafe.BitCast? I see that Unsafe.BitCast is restricted to struct and doesn't require a ref, but they both do the same thing: reinterpret the bits of the target. What's the practical difference?

[tannergooding]

Unsafe.BitCast works on value types and doesn't require taking an address, which can improve the overall codegen/perf in some complex scenarios (in simple ones the JIT will normally recognize its not actually "address-taken").

It also helps guarantee correctness as it also requires the input/output be the same size and therefore that you aren't accessing bits that don't exist.