Feature request: `extract_if`

[CastilloDel]

Would it be possible to implement an efficient drain_filter method for the IndexMaps and IndexSets that behaves like the one in std?

[cuviper]

Ideally, we would wrap Vec::drain_filter, since that's how we store our items, but that method is still unstable. I'm not sure how hard it would be to redo that ourselves, but we do similar for the MSRV lack of Vec::retain_mut already. Then we would probably just rebuild the entire RawTable if anything was removed, just like we do for retain.

The other thing about drain_filter being unstable is that we generally want to match std's API here as much as possible, but that's subject to change until it's finally stabilized.

[CastilloDel]

The other thing about drain_filter being unstable is that we generally want to match std's API here as much as possible, but that's subject to change until it's finally stabilized.

That makes sense, I guess it will be better for indexmap to wait until the API stabilizes

[cuviper]

Note that rust-lang/rust#59618 renamed it to extract_if.

I've opened a draft at #308, but I still want to wait for std to stabilize the API. I'm not using std in my implementation though, so we won't need to worry about MSRV.

[MatrixDev]

extract_if was finally stabilized.
Would it now be possible to add similar implementation for IndexMap or should we wait when it hits a stable rust?

[cuviper]

I've kept #308 up to date, but yes, I plan to wait for stable. Rust 1.87 will be on May 15th -- the 10 year anniversary!

[cuviper]

While Vec::extract_if made it in 1.87, the map and set methods were delayed to 1.88 (due June 26):
rust-lang/rust#139765

[reneleonhardt]

They have been stabilized, the wait is over 🚀
https://blog.rust-lang.org/2025/06/26/Rust-1.88.0/#stabilized-apis