Merge pull request #1 from Ericson2314/fn-lifetime

Add unresolved question of `break 'fn ..`

text/0000-fn-lifetime.md

@@ -68,4 +68,19 @@ What other designs have been considered? What is the impact of not doing this?
 # Unresolved questions
 [unresolved]: #unresolved-questions
 
+- Should we allow `break 'fn ..` with the same semantics as `return ..`. In
+ [RFC 1624](https:/rust-lang/rfcs/blob/master/text/1624-loop-break-value.md)
+ we got breaking with a value out of loops, so the value part is already
+ established. This provides one canonnical syntax for breaking out of a loops
+ or functions, leaving `return` just a convenience. In a future with full
+ lifetime ascription, this would further generalize to supporting all labeled
+ blocks, not just loops and functions.
+
+ A downside is `continue 'a` will still only make sense when `'a` is bound to a
+ loop, and `break 'a` won't make sense when `'a` is a lifetime parameter. That
+ means users will need to understand their are three tiers of lifetimes: loop,
+ block (including `'fn`), and, parameter, where each is less usable than the
+ last. Today loop lables and lifetimes are disjoint in that neither can be used
+ where the other is expected, though they do share the same syntax.
+
 What parts of the design are still TBD?