ArrayVec is undefined behavior when storing types with invalid bit patterns

[orlp]

Initially in an ArrayVec the memory is uninitialized: https://github.com/bluss/arrayvec/blob/master/src/lib.rs#L80.

This simply is UB in Rust for any types with invalid bit patterns (most notably references). Just creating an uninitialized value with these bit patterns is UB.

Even perfectly fine code that never actually reads or uses the uninitialized memory still has undefined behavior. I ran into this myself: https://stackoverflow.com/questions/52348277/vector-is-empty-after-cloning-struct-with-uninitialized-member.

[bluss]

Thanks, this is something that has clarified a lot in recent versions of Rust, and we should be able to use MaybeUninitialized soon.

[bluss]

See also #97 and related issues and prs

[bluss]

Closed by #127 with the caveat, that Rust 1.36 or later is required.