LLVM assert with explicit self and objects

[brson]

pub trait Reader {
    // FIXME (#2004): Seekable really should be orthogonal.

    /// Read up to len bytes (or EOF) and put them into bytes (which
    /// must be at least len bytes long). Return number of bytes read.
    // FIXME (#2982): This should probably return an error.
    fn read(&self, bytes: &[mut u8], len: uint) -> uint;
}

pub trait ReaderUtil {

    /// Read len bytes into a new vec.
    fn read_bytes(&self, len: uint) -> ~[u8];
}

impl<T: Reader> T : ReaderUtil {

    fn read_bytes(&self, len: uint) -> ~[u8] {
        let mut bytes = vec::with_capacity(len);
        unsafe { vec::raw::set_len(&mut bytes, len); }

        let count = (&*self).read(bytes, len);

        unsafe { vec::raw::set_len(&mut bytes, count); }
        move bytes
    }

}

impl int: Reader {
    fn read(&self, bytes: &[mut u8], len: uint) -> uint {
        0
    }
}

fn main() {
    let x = @0;
    let x = x as @Reader;
    x.read_bytes(0);
}

rustc: /home/brian/dev/rust/src/llvm/include/llvm/Instructions.h:705: llvm::Type* llvm::checkGEPType(llvm::Type*): Assertion `Ty && "Invalid GetElementPtrInst indices for type!"' failed.

[kvark]

I'd really like to know how to work around this on Rust-0.4. A shorter code sample:

trait Element {
    fn draw( &self );
}
struct Frame {
    element : @Element,
}
impl Frame {
    fn draw_all() {
        self.element.draw();
    }
}
fn main() {}

[graydon]

(works in 0.5)