wtf, rust?

gistfile1.txt

// Config.rs:34

fn save_PrettyJSON<'a, T: Encodable<json::PrettyEncoder<'a>>>(p: &Path, toEncode: ~[T]) {
    match File::create(p) {
        Some(f) => {
            let f2 = @mut f as @mut io::Writer;
            let a = &mut json::PrettyEncoder::init(f2);
            toEncode.encode(a);
        }, None => fail!("failed to save json")
    };
}

// DOESN'T work:
fn save_PrettyJSON<'a, T: Encodable<json::PrettyEncoder<'a>>>(p: &Path, toEncode: ~[T]) {
    match File::create(p) {
        Some(f) => {
            let mut f2 = f;
            let a = &mut json::PrettyEncoder::init(
                @mut f2 as @mut io::Writer);
            toEncode.encode(a);
        }, None => fail!("failed to save json")
    };
}

// WORKS:
fn save_PrettyJSON<'a, T: Encodable<json::PrettyEncoder<'a>>>(p: &Path, toEncode: ~[T]) {
    match File::create(p) {
        Some(f) => {
            let mut f2 = f;
            let a = &mut json::PrettyEncoder::init(
                &mut f2 as &mut io::Writer);
            toEncode.encode(a);
        }, None => fail!("failed to save json")
    };
}

(gdb) thread apply all bt

Thread 9 (Thread 0x7ffff4efb700 (LWP 16244)):
#0  0x00007ffff74bc03f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0
#1  0x0000000000576f69 in uv_cond_wait (cond=cond@entry=0xf1e6e0 <cond>, 
    mutex=mutex@entry=0xf1e6a0 <mutex>) at ../../../src/libuv/src/unix/thread.c:324
#2  0x0000000000577183 in worker (arg=arg@entry=0x0) at ../../../src/libuv/src/unix/threadpool.c:56
#3  0x00000000005792e7 in uv__thread_start (arg=<optimized out>)
    at ../../../src/libuv/src/uv-common.c:274
#4  0x00007ffff74b80a2 in start_thread () from /usr/lib/libpthread.so.0
#5  0x00007ffff6cd049d in clone () from /usr/lib/libc.so.6

Thread 8 (Thread 0x7ffff56fc700 (LWP 16243)):
#0  0x00007ffff74bc03f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0
#1  0x0000000000576f69 in uv_cond_wait (cond=cond@entry=0xf1e6e0 <cond>, 
    mutex=mutex@entry=0xf1e6a0 <mutex>) at ../../../src/libuv/src/unix/thread.c:324
#2  0x0000000000577183 in worker (arg=arg@entry=0x0) at ../../../src/libuv/src/unix/threadpool.c:56
#3  0x00000000005792e7 in uv__thread_start (arg=<optimized out>)
    at ../../../src/libuv/src/uv-common.c:274
#4  0x00007ffff74b80a2 in start_thread () from /usr/lib/libpthread.so.0
#5  0x00007ffff6cd049d in clone () from /usr/lib/libc.so.6

Thread 7 (Thread 0x7ffff5efd700 (LWP 16242)):
#0  0x00007ffff74bc03f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0
#1  0x0000000000576f69 in uv_cond_wait (cond=cond@entry=0xf1e6e0 <cond>, 
    mutex=mutex@entry=0xf1e6a0 <mutex>) at ../../../src/libuv/src/unix/thread.c:324
---Type <return> to continue, or q <return> to quit---
#2  0x0000000000577183 in worker (arg=arg@entry=0x0) at ../../../src/libuv/src/unix/threadpool.c:56
#3  0x00000000005792e7 in uv__thread_start (arg=<optimized out>)
    at ../../../src/libuv/src/uv-common.c:274
#4  0x00007ffff74b80a2 in start_thread () from /usr/lib/libpthread.so.0
#5  0x00007ffff6cd049d in clone () from /usr/lib/libc.so.6

Thread 6 (Thread 0x7ffff66fe700 (LWP 16241)):
#0  0x00007ffff74bc03f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0
#1  0x0000000000576f69 in uv_cond_wait (cond=cond@entry=0xf1e6e0 <cond>, 
    mutex=mutex@entry=0xf1e6a0 <mutex>) at ../../../src/libuv/src/unix/thread.c:324
#2  0x0000000000577183 in worker (arg=arg@entry=0x0) at ../../../src/libuv/src/unix/threadpool.c:56
#3  0x00000000005792e7 in uv__thread_start (arg=<optimized out>)
    at ../../../src/libuv/src/uv-common.c:274
#4  0x00007ffff74b80a2 in start_thread () from /usr/lib/libpthread.so.0
#5  0x00007ffff6cd049d in clone () from /usr/lib/libc.so.6

Thread 2 (Thread 0x7ffff7f49700 (LWP 16237)):
#0  0x00007ffff6ccc379 in syscall () from /usr/lib/libc.so.6
#1  0x0000000000571d9a in uv__epoll_wait (epfd=<optimized out>, events=events@entry=0x7ffff7f45b70, 
    nevents=nevents@entry=1024, timeout=timeout@entry=-1)
    at ../../../src/libuv/src/unix/linux-syscalls.c:282
#2  0x000000000057066e in uv__io_poll (loop=loop@entry=0xf22010, timeout=-1)
    at ../../../src/libuv/src/unix/linux-core.c:168
#3  0x000000000056bd27 in uv_run (loop=0xf22010, mode=UV_RUN_DEFAULT)
    at ../../../src/libuv/src/unix/core.c:276
---Type <return> to continue, or q <return> to quit---
#4  0x000000000050b1a6 in rt::sched::Scheduler::run::h826c184529eecf45SAa3::v0.9$x2dpre ()
#5  0x000000000049eea2 in rt::sched::Scheduler::bootstrap::h19e397cb2dfd268SAat::v0.9$x2dpre ()
#6  0x00000000005226aa in rt::run_::anon::expr_fn::aH ()
#7  0x000000000049d745 in rt::thread::Thread::start::anon::expr_fn::Tfa8ad ()
#8  0x000000000050f574 in rt::thread::thread_start::h65f2b6e99a9c1b16aP::v0.9$x2dpre ()
#9  0x00007ffff74b80a2 in start_thread () from /usr/lib/libpthread.so.0
#10 0x00007ffff6cd049d in clone () from /usr/lib/libc.so.6

Thread 1 (Thread 0x7ffff7fbc740 (LWP 16233)):
#0  0x00007ffff74b94a2 in pthread_join () from /usr/lib/libpthread.so.0
#1  0x000000000049ba07 in rt::thread::native_thread_join::ha56a78a194f6e1b6a3::v0.9$x2dpre ()
#2  0x000000000049d264 in rt::thread::Thread::join::h42b183f056dbd22ZCaG::v0.9$x2dpre ()
#3  0x000000000052000c in rt::run_::he81a23d5f9cf1151aV::v0.9$x2dpre ()
#4  0x00000000004fcac2 in unstable::lang::start::h3f962587acaf2991a3::v0.9$x2dpre ()
#5  0x00007ffff6c0cbc5 in __libc_start_main () from /usr/lib/libc.so.6
#6  0x0000000000407471 in _start ()
(gdb) 

#[feature(managed_boxes)];

struct Whatever<'a> { w: &'a mut std::io::Writer }
impl <'a> Whatever<'a> {
    fn new<'b>(w: &'b mut std::io::Writer) -> Whatever<'b> {
        Whatever { w: w }
    }
}

fn save_PrettyJSON(p: &Path) {
    match std::io::File::create(p) {
        Some(f) => {
            let mut f2 = f;
            let a = &mut Whatever::new(@mut f2 as @mut std::io::Writer);
        },
        None => fail!()
    };
}

fn main() {
    save_PrettyJSON(&Path::init("sntahoeu"));
}

#[feature(managed_boxes)];

struct DroppableStruct;
impl Drop for DroppableStruct {
    fn drop(&mut self) {
        println!("Dropping");
    }
}

trait MyTrait { }
impl MyTrait for DroppableStruct {}


struct Whatever<'a> { w: &'a mut MyTrait }
impl <'a> Whatever<'a> {
    fn new<'b>(w: &'b mut MyTrait) -> Whatever<'b> {
        Whatever { w: w }
    }
}

fn main() {
    let mut f = DroppableStruct;
    let _a = &mut Whatever::new(@mut f as @mut MyTrait);
}