Memoized selectors: proxy-memoize or useShallow?

[alexander-ye]

Question about writing memoized selectors when using zustand:

I see that useShallow is recommended above shallow (#2203) to prevent rerenders.

But I also know that proxy-memoize is an option for writing memoized selectors.

What is the recommended approach here? I've read a thread that says that shallow is "easier", but I'm wondering if there a difference between using the two? (Does useShallow use proxy-memoize under the hood?) If so, which one is recommended/more performant?

Thanks!

[dai-shi]

The goals are a little different:

• shallow (or useShallow) is to compute again and compare the result. It's good and easy if re-computing is lightweight.
• proxy-memoize (or other memoization techniques/libs) is to avoid re-computation completely. So, it's good if the computation is heavyweight, but it comes with some cost.

[alexander-ye]

Awesome, thanks!

So, if I'm understanding correctly:

• shallow (or useShallow) runs an equality comparison function that gets expensive the more expensive the return object is—and it's an expense on top of what might be a potentially expensive computation.
• proxy-memoize is similar to useMemo in that it only runs when a dependency (in this case, argument object reference) changes—but it has the overhead of setting up the dependency/argument equality "listeners."