Unsafe blocks make their contents pure?

[brson]

This came from a pull request recently:

pure fn ln(n: float) -> float { unsafe { libc::ln(n) } }

I would expect that 'unsafe' block to be an 'unchecked' block.

[nikomatsakis]

purity and unsafety are not orthogonal. At first I thought they ought to be but it made a lot of things harder and I couldn't think of a good reason to support it. So functions are either normal, pure, or unsafe. As a side effect, an unsafe block is like an unchecked block but stronger. I am not sure this is how it should be, but it's not an accident per se.

[brson]

Yes, I remember that decision now. Closing.