Unconstrained region variables when making str-ptr-ptr hash and eq

@nikomatsakis

Test case:

pure fn view_hash(s: & &str) -> uint {
    hash::hash_str(*s) as uint
}

pure fn view_eq(a: & &str, b: & &str) -> bool {
    str::eq_slice(*a, *b)
}

fn main() {
    let map = send_map::linear::linear_map(view_hash, view_eq);
    map.insert("foo", ());
}

Errors:

/home/pcwalton/Source/rust/build/test.rs:11:58: 11:65 error: Unconstrained region variable #3
/home/pcwalton/Source/rust/build/test.rs:11         let map = send_map::linear::linear_map(view_hash, view_eq);
                                                                                                      ^~~~~~~
/home/pcwalton/Source/rust/build/test.rs:11:58: 11:65 error: Unconstrained region variable #4
/home/pcwalton/Source/rust/build/test.rs:11         let map = send_map::linear::linear_map(view_hash, view_eq);

If the functions become inline lambdas, the problem goes away.

@nikomatsakis, any ideas?

I was fiddling around with regioned stack closures, trying to see if it'd ever mean something to return one, and ran into the same error for the first time:

fn foo(+blk: fn(+p: &a/fn() -> &a/fn())) {
    let mut state = 0;
    let statep = &mut state;
    do blk {
        || { *statep = 1; }
    }
}
fn main() {
    do foo |p| { p()() }
}


frames.rs:1:0: 1:0 error: Unconstrained region variable #8
frames.rs:1 fn foo(+blk: fn(+p: &a/fn() -> &a/fn())) {
            ^
frames.rs:1:0: 1:0 error: Unconstrained region variable #10
frames.rs:1 fn foo(+blk: fn(+p: &a/fn() -> &a/fn())) {
            ^

@pcwalton

@pcwalton 's example no longer works since the linear_map function being used is now trait-based, rather than taking functions explicitly. I get a different error with @bblum's example:

/Users/tchevalier/rust2/src/test/run-pass/issue-3283.rs:4:11: 6:5 error: mismatched types: expected `&fn()` but found `@fn()` (expected & closure, found @ closure)
/Users/tchevalier/rust2/src/test/run-pass/issue-3283.rs:4     do blk {
/Users/tchevalier/rust2/src/test/run-pass/issue-3283.rs:5         || { *statep = 1; }
/Users/tchevalier/rust2/src/test/run-pass/issue-3283.rs:6     }

I don't know if that's right or not.

bblum's example compiles now (if you add a & before the fn type of blk), and pcwalton's example won't compile now for other reasons. So I'm considering this done. Reopen if you have a repro case

bblum's example compiled and ran just fine on my Mac, but segfaulted on the Linux and Windows bots. I don't have time right now to figure out why, so I'm checking it in xfailed.

I think this system should not type check. This is probably a bug in how we are handling region closures (I know there is work to be done there, not sure what bug #, let me fish it up).

Dup of issue #3696, I think.

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Unconstrained region variables when making str-ptr-ptr hash and eq #3283

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Unconstrained region variables when making str-ptr-ptr hash and eq #3283

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bblum commented on Aug 26, 2012

catamorphism commented on Dec 7, 2012

catamorphism commented on Mar 20, 2013

catamorphism commented on Mar 25, 2013

nikomatsakis commented on Mar 29, 2013

nikomatsakis commented on Mar 29, 2013

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