All vec.rs by-reference functions are unsafe.

[bblum]

For example, fn push<T>(&v: ~[const T], +initval: T) -- has a huge unsafe block inside, and might mutate the caller's "v" pointer.

This is... maybe safe today, but not in theory, and will break with rw_arcs (#3145).

[bblum]

Never mind; they are fine. Just be careful with them when converting away from argument modes.