Add LoadOrTryCompute method

[mattjohnsonpint]

#103 describes how to raise an error if Compute fails. In that example, return 0, true ensures that the 0 is not added to the map.

That works fine for Compute, but I don't see a similar approach possible for LoadOrCompute - since the valueFn doesn't have a delete return value.

So, when using LoadOrCompute, how can I ensure that if an error occurs that I don't add a zero value (or nil, etc.) to the map? I wouldn't want a concurrent thread to retrieve that and treat it as an actual good value.

TLDR: Can you please add a version of LoadOrCompute that accepts a valueFn func() (newValue V, delete bool)?

Thanks.

[puzpuzpuz]

Compute is flexible enough to be used in LoadOrCompute style, so you could use it instead of LoadOrCompute:

counts := xsync.NewIntegerMapOf[int, int]()

v, ok := counts.Compute(42, func(oldValue int, loaded bool) (newValue int, delete bool) {
	if loaded {
		return oldValue, false // return the existing value
	}
	// the error-aware logic goes here
	return
})

Does this make sense?

[puzpuzpuz]

Closing this one as it's been as is for a while. Feel free to comment if something is unclear.

[mattjohnsonpint]

Sorry for the delay. Yes, I can make Compute work, if in the case of an error I return 0, true. However, if I'm interpreting the comments correctly, Compute is taking a full lock with each call. So there's a perf implication. I can reduce this by using Load first, but that feels a lot like double-checked locking, which I'd like to avoid. Isn't that the point of LoadOrCompute?

[puzpuzpuz]

Ok, I understand the use case now: you want to be able to skip adding a computed value. Sounds like you need a new method like LoadOrComputeIf or LoadOrTryCompute. I'll add it in one of the upcoming versions.

[mattjohnsonpint]

LoadOrTryCompute sounds perfect. Thanks!