fix: allow object options to share the same label

[GauBen]

Closes #216

Keys can be objects, though somewhat discouraged.

The key can be any object, but strings and numbers are recommended since they allow identity to persist when the objects themselves change.

[janosh]

I thought keys have to be primitive types?

[janosh]

Ah, I was wrong. From the Svelte docs:

You can use any object as the key, as Svelte uses a Map internally — in other words you could do (thing) instead of (thing.id). Using a string or number is generally safer, however, since it means identity persists without referential equality, for example when updating with fresh data from an API server.

[GauBen]

Svelte uses a Map under the hood, objects are legal keys but can have unexpected side effect, that's why the doc discourage non primitive keys

Edit: ahahah you were faster

[janosh]

Maybe we should still default to the option label as key but allow overriding this behavior by exposing a new prop get_key: (option: Option) => unknown = get_label?

[GauBen]

That's a an option too, but having two different values with the same name would still break svelte-multiselect

[janosh]

That's true but that was by design (until now anyway). Maybe it's not a good default. I think I made that decision at the time because I couldn't think of a strong use case for duplicate options. That was before allowing user-created options. But even now, maybe it's better to show a warning to users rather than allowing them to make duplicate options?

[GauBen]

That's right, shall I update this PR with a new get_key option? Or are you ok with option being used as an index?

The only thing that might break with the current PR is animate:flip when selected is updated by copy and not reference

https://svelte.dev/repl/60e7b5893b304b8f9e0ea094fe6bb293?version=3.57.0

(just updated the repl with both kind of copies)

[janosh]

The only thing that might break with the current PR is animate:flip when selected is updated by copy and not reference

I didn't realize the downside was this small. Nice REPL btw. Very educational.

That's right, shall I update this PR with a new get_key option?

No, I'm sold. I think we should just add a test that covers selecting two identical object options.

[GauBen]

Thanks for the quick merge!