`try!(foo)` is roughly equivalent to this (invalid) code:

    foo().unwrap_or_else({ |e| return Err(e) })

Or in Go terms:

    a := try!(foo)

is equivalent to:

    a, err := foo()
    if err != nil {
        return nil, err
    }

Basically it will take the result of foo, and if foo returns an error it will return the error itself.

https://doc.rust-lang.org/beta/std/result/ has lots of examples of alternative ways you can deal with the error case, or the Ok() case of a result.