KBString for byte strings?

[joshtriplett]

I'd love to have a version of KString that can hold arbitrary bytes, rather than UTF-8. I currently use BString, but I'd love to have the compact string optimization of KString.

[epage]

Are you looking for just a compact Vec<u8> and willing to pull in bstr for ByteSlice trait or are you looking for us to implement all of the relevant string methods?

If you are fine with ByteSlice then this would be relatively trivial to get in and I've been considering byte/OsStr versions.

[Byron]

This enhancement would be very relevant for gix-attributes, which has short keys (attribute names) that fit into UTF-8, and values which can take most values and thus are better represented as byte strings (like bstr). For now I will go with String/bstr::BString here and leave everything else to future profiler driven optimizations.

[Byron]

I ended up doing something like this:

/// A reference container to encapsulate a tightly packed and typically unallocated byte value that isn't necessarily UTF8 encoded.
#[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone, Copy)]
pub struct ValueRef<'a>(KStringRef<'a>);

/// Conversions
impl<'a> ValueRef<'a> {
    /// Keep `input` as our value.
    pub fn from_bytes(input: &'a [u8]) -> Self {
        Self(KStringRef::from_ref(
            // SAFETY: our API makes accessing that value as `str` impossible, so illformed UTF8 is never exposed as such.
            #[allow(unsafe_code)]
            unsafe {
                std::str::from_utf8_unchecked(input)
            },
        ))
    }

    /// Access this value as byte string.
    pub fn as_bstr(&self) -> &BStr {
        self.0.as_bytes().as_bstr()
    }
}

I am writing this here just to assure myself that KBString/KBStringRef don't rely on valid UTF8 for inline storage. Tests indicate that everything works fine.