Suppliers.memoize should return a MemoizingSupplier with isMemoized()

[alexey-pelykh]

API(s)

`com.google.common.base.Suppliers::memoize`

How do you want it to be improved?

Get memoizing supplier state without causing memoization

Why do we need it to be improved?

To check the memoizing supplier state without changing it

Example

N/A as there's no such feature

Current Behavior

MemoizingSupplier::initialized is not exposed

Desired Behavior

MemoizingSupplier::initialized is exposed

Concrete Use Cases

e.g. in toString() of a class that needs to print a memoized supplier value without causing the memoization

Checklist

• [X] I agree to follow the code of conduct.

• [X] I have read and understood the contribution guidelines.

• [X] I have read and understood Guava's philosophy, and I strongly believe that this proposal aligns with it.

[cgdecker]

e.g. in toString() of a class that needs to print a memoized supplier value without causing the memoization

Does the default toString() of the memoizing supplier not work for you? It doesn't trigger the memoization if it hasn't occurred yet.

My inclination is that this is niche enough that I'd suggest just writing your own, perhaps even wrapping a single-element LoadingCache or something.

[alexey-pelykh]

While toString() use-case could be mitigated, I fail to see how exposing a property that's already there can be harmful. Currently I have to resort to using Apache Commons because there's LazyInitializer.html#isInitialized - however I find it's usage bulky in comparison to MemoizingSupplier.