Embedded indexes

[OvermindDL1]

Say I have a mock-up like this:

struct Inner {
  blah: String,
  more: String
}

#[derive(MultiIndexMap)]
struct Outer {
  #[multi_index(hashed_unique)]
  id: String,
  #[multi_index(hashed_unique)]
  inner: Inner,
}

Except for the inner I'm not wanting 'it' to be hashed, rather I want the inner.blah to be hashed, what about being able to specify something like #[multi_index(hashed_unique, extract = "&self.inner.blah")] or so for an extraction expression (with the documentation of course that it should be fast and always return the same value). Maybe better belong on the struct itself like #[multi_index(indexes = {blah: "&self.inner.blah"})] or something like that so it can have a more appropriate index name as well.

In addition, an index embedded in an Option, like say inner: Option<Inner> it would be nice to be an optional unique index, so it's a unique index if it exists, but if it doesn't exist then it's not part of that index at all.

[OvermindDL1]

In addition, it also doesn't seem to use Borrow for the key value like std's HashMap and so forth use either, so we have to actually construct the full key instead of just a borrowed value of it (like being able to look up with a &str instead of a full heap allocated &String).

[lun3x]

Hey, thanks I like the second idea! I've implemented the logic for this, and will make a release with this soon. Unfortunately I think the first idea adds too much complexity to this library, so I am closing this issue for now.