Implement a .len() function

[jmg-duarte]

I'm currently using this crate for "incremental" options for an application I'm writing - to that end, I need to iterate over the set flags in the structure.

I've started implementing an iterator which simply goes through the bits, right to left and yields an Option<BitFlag> for each, signaling whether it is set or not - to achieve this, having a length method in the generated structure would help immensely since it allows me to know when I've reached the structure end.

Would there be interest in implementing this?

[jmg-duarte]

I've written a "workaround" .len():

const fn len() -> usize {
    let mut all = Self::all().bits();
    let mut idx = 0;
    while all != 0 {
        all >>= 1;
        idx += 1;
    }
    idx
}

[KodrAus]

Hi @jmg-duarte 👋

This unfortunately starts to get tricky when you have flags that cover multiple bits, which is something that bitflags allows even if it's not the most common case. I think that's what's stalled most attempts to implement a general iterator for all kinds of flags. The latest attempt is #278, which seems pretty close.

[KodrAus]

Since #278 is merged we can now write flags.iter().count(). I think this is nice and clear and communicates that the length you get is calculated rather than intrinsic.

We're currently working towards a 2.0.0 release that will include this and some other breaking changes for better future-proofing. If you'd like to keep track of where that's at you can follow along #262