Ports and channels tutorial example code

[jesse99]

Has code like comm::port::<int>() which looks odd and seems erroneous.

[marijnh]

This is perfectly correct code, though.

[jesse99]

It hasn't worked anywhere I have tried it. It fails with this code for example:

import comm;

fn main(args: [str])
{
let port1: comm::port = comm::port();
port1;

// get hello.rs:9:21: 5:23 error: expecting ';' but found '::'
let port2: comm::port::<int> = comm::port();
port2;

args;

}

compiled with rustc -o hello hello.rs. This is with commit:0904f255075d3c20f16d4ca2d1db14cac3fbb2de (which is a few days past 0.2).

[jesse99]

Here's the example again (github thought some of the code was markup):

import comm;

fn main(args: [str]) 
{
    let port1: comm::port<int> = comm::port();
    port1;

    // get hello.rs:9:21: 5:23 error: expecting ';' but found '::'
    let port2: comm::port::<int> = comm::port();
    port2;

    args;
}```

[marijnh]

That's not code from the tutorial, is it?

In value expressions (comm::port::<int>()), type parameters have to be prefixed with :: to prevent ambiguity with the < operator. In type expressions (such as : comm::port<int>), they shouldn't be.

We are aware of the fact that this is confusing (I think there's a bug open on it, though I can't find it just now), but we haven't been able to find a satisfactory alternative.

[jesse99]

No, that code wasn't from the tutorial. And, yes the difference is confusing, especially because the tutorial doesn't point out the distinction. Not sure if the reference manual does. I spent a few minutes looking and didn't find anything.

[marijnh]

For what it's worth, section 8.3 of the tutorial does point out this distinction.