Unexpected / uneccessary store.set calls when binding values from a store

[Prinzhorn]

Describe the bug

When you bind: values from a store inside #each it will call set for every iterated item for no reason. I'm using this pattern a lot where I have a store (that is backed by sessionStorage, synced via BroadcastChannel and persisted via fetch()). I love how I can pass values from inside a store around, then child components can update them and everything magically works across windows and is persisted between app restarts (Electron).

But I've just ran into an edge case where I'm seeing a lot of completely unnecessary calls to set, causing pointless disk and network I/O. Since this is happening inside #each there can easily be dozens of set for each item I bind to.

To Reproduce

I wrapped the set method so it logs every call. When you open this REPL you'll see two set calls for no reason.

https://svelte.dev/repl/1e967d0310c3428989dde2ec1bf70087?version=3.38.2

Expected behavior

There is no reason to call set when there was no change.

Information about your Svelte project:

REPL 3.38.2

Severity

Medium. I'll probably have to workaround this by sprinkling some fast-deep-equal over my stores.

[Prinzhorn]

I'll probably have to workaround this by sprinkling some fast-deep-equal over my stores.

Nope, that doesn't generically work, because the point is that I work with mutable objects. I update a property deep inside an object that is held by a store and then call set to notify everyone (or like in this issue bind does that for me). Checking for equality is always true because it's the same reference.

[Prinzhorn]

Thanks to #6590 I can confirm that this is not related to #each and repros without it, bind: just seems to trigger an unnecessary update.

Updated REPL with 3.41.0 will log a store.set call https://svelte.dev/repl/1e967d0310c3428989dde2ec1bf70087?version=3.41.0

[dummdidumm]

Likely the same underlying reason as for #5689

[SiaEmgee]

It is about the binding data being an 'object' .
primitive and object comparison :
https://svelte.dev/repl/a58cf5f308904c02b34d0a26f3a4e9fa