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proc bounds and closure lifetimes are parsed incorrectly #10553
Description
<kimundi> If you have a function that takes a reference to a closure the lifetime specifier becomes confusing
<kimundi> fn foo(&|T| -> U), fn foo(&'a |T| -> U) and fn foo(&'a 'a |T| -> U) are all valid, and in the second one you can't tell which one of both the lifetimes is supposed to belong to
<nmatsakis> kimundi: this is parser bug, 'a |T| shouldn't parse
<nmatsakis> it should be |T|:'a
<nmatsakis> the parser may well be wrong
<nmatsakis> maybe got overlooked
<kimundi> well, if I change to that syntax I get compile errors
<kimundi> this works: impl<'a> StringPrefixMatch for 'a |$self_anon| -> bool
<kimundi> this doesn't: impl<'a> StringPrefixMatch for |$self_anon|:'a -> bool
<kimundi> I get a "'static is the only valid region allowed here" error
<nmatsakis> kimundi: I think it's just a parser bug
<nmatsakis> kimundi: yes, I can understand why that would occur
<kimundi> why?
<nmatsakis> kimundi: basically because some cleanup is needed
<nmatsakis> we are interpreting |...|:K with K as a list of bounds , which is correct,
<nmatsakis> but we currently haven't implemented support for arbitrary lifetimes in bounds,
<nmatsakis> which is wrong,
<nmatsakis> and instead we have special case treatment for closures,
<kimundi> Ah, so it only accepts the 'static bound there
<nmatsakis> which kind of fit ok with the old syntax,
<nmatsakis> but in the newer one we really should be just using general lifetimes in bounds
Activity
Kimundi commentedon Nov 18, 2013
cc @nikomatsakis
pnkfelix commentedon Dec 2, 2013
cc me
pnkfelix commentedon Dec 12, 2013
Note in particular that attempting to make
'a |T| -> Ua type expression leads to ambiguities when parsing a generic instantiation where you are trying to pass a closure type as the type parameter, likeFoo<'a |T| -> U>, because the parser will eagerly treat theFoo<'aprefix as a lifetime parameter being passed toFoo, and thus it expects a comma next.(An easy work-around for the type being is to use a
typedeclaration liketype closure<'a, T, U> = 'a |T| -> U;and then you can instantiate
Fooon the typeclosure<'a, T, U>.)flaper87 commentedon Jan 30, 2014
cc @flaper87
nikomatsakis commentedon Feb 27, 2014
Another parser issue: something like
proc:Senddoesn't parsenikomatsakis commentedon Feb 27, 2014
Nominating.
pnkfelix commentedon Feb 27, 2014
Assigning 1.0, P-backcompat-lang
emberian commentedon Feb 27, 2014
cc me
nikomatsakis commentedon Feb 27, 2014
For reference, I believe the syntax ought to be:
nikomatsakis commentedon Feb 27, 2014
Except of course that parameter lists are comma-separated
alexcrichton commentedon Feb 27, 2014
I'm assuming that with that syntax you can also have multiple
Kvalues+-separate? Would I be correct in these translations:17 remaining items
auto merge of #13268 : alexcrichton/rust/parse-closure, r=cmr
Auto merge of rust-lang#10553 - Nilstrieb:better-uninit, r=Alexendoo
Merge rust-lang#10555