Consider using associated constants for the bitflag-like types

[dtolnay]

The various Ready constructors currently work like this:

impl Ready {
    pub fn readable() -> Ready { /* ... */ }
    pub fn writable() -> Ready { /* ... */ }
}

With the associated constants feature of Rust 1.20, it could work like this:

impl Ready {
    pub const READABLE: Ready = /* ... */;
    pub const WRITABLE: Ready = /* ... */;
}

The constructors never do any work so they shouldn't need to be functions.

One advantage of constants is that they can be used in the pattern of a match statement.

[AndyGauge]

I want to learn the associated constraints feature, so I'm going to give this a shot.

[dtolnay]

Great! Go for it. When it is done we will need to evaluate whether it is really an improvement over the current way.

[AndyGauge]

So one problem with using Associated Constants is that it breaks previous builds of Rust. Currently, Travis tests version 1.13 which will fail with the implementation of the feature. I also wanted to capture @carllerche comment about now that rustc 1.20 has dropped, the feature can be implemented in 12 weeks (12/24ish).

[dethoter]

I'm wondering why do you use struct(usize) and a number of associated constants instead of a plain enum?

[carllerche]

Mio will move away from bitflag style APIs in 0.7. This issue is no longer relevant.