Inserting a value into HashSet getting a reference to it

Asked Apr 19 '19 at 13:49

Active Apr 19 '19 at 13:49

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I need to refer to a value after inserting it into set. However after inserting the container becomes the owner of the element and I can no longer refer to it. Is this achievable without updating the containers API?

Ideally I'm looking for some function with the following signature:

fn insert_referring<A>(set: &mut HashSet<A>, element: A) -> &A

asked Apr 19 '19 at 13:49

Nikita Volkov

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You can wrap your objects into a `Rc`. – Boiethios Apr 19 '19 at 13:52
That would work, but would also incur overhead. I hope to find a solution, which wouldn't. – Nikita Volkov Apr 19 '19 at 13:57
I'm with you: unfortunately, I think that this would require a new method. – Boiethios Apr 19 '19 at 14:00
In your situation, I would use a `HashMap` to retrieve the value easily. – Boiethios Apr 19 '19 at 14:01
Can you clear this out as an answer possibly? – Nikita Volkov Apr 19 '19 at 14:03
Are you looking for something like this? [Playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=b39ea14bea827fb135914776207bc6da) – Akiner Alkan Apr 19 '19 at 14:06
You can refer to the value from the `HashSet` using [`get`](https://doc.rust-lang.org/stable/std/collections/struct.HashSet.html#method.get). However this requires an additional lookup. I don't think there is a way to do it in a single step. – Jmb Apr 19 '19 at 14:08
You should create an issue to add this. – Boiethios Apr 19 '19 at 14:14
A `HashSet` is a `HashMap`; thus the duplicate – Shepmaster Apr 19 '19 at 14:30
@NikitaVolkov I mean, you could create your own handle as a key to retrieve the value easily, but that's specific to your need. – Boiethios Apr 19 '19 at 14:30

Inserting a value into HashSet getting a reference to it

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