On 11-07-14 12:44 PM, Marijn Haverbeke wrote:
I don't understand how the alias checker figures into it. It's a lifetime
thing. How do you ensure the aliased value remains live as long as the alias
does?
Right, I was too vague on that. You can only return aliases that are
'rooted' (by the rules I explained in the previous alias-checking
discussion) in arguments to the current function that were passed by
alias. This ensures that the alias is still live when returned. (It
might in some situations be difficult to prove this rooting, I haven't
thought too deeply about that yet.)
Ok. Slightly more plausible...
On the callee side, the alias checker knows that the returned alias is
rooted in one of the arguments passed to the call that created it.
Sometimes it can pinpoint the exact argument using type analysis (an
int won't root a str, and only stuff passed by alias must be
considered). It then disallows 'displacement' (overwriting, moving out
of, or for mutable containers, taking the value of) of these roots
until the last use of the returned alias.
Disallows ... on the *caller* side as well? How far out can the alias go?
-Graydaon
_______________________________________________
Rust-dev mailing list
Rust-dev@mozilla.org
https://mail.mozilla.org/listinfo/rust-dev
