detecting approximateSize presence

[mcollina]

approximateSize support is not widespread: MemDOWN and Level.js do not have it.

However, this interface do not provide a way for knowing if that support is there or not.

We need it for levelgraph/levelgraph#23.

[rvagg]

So, I think we've deprecated db.approximateSize() in LevelUP in favour of db.db.approximateSize(), along with the other LevelDB-specific stuff. My preference would be to remove the tests from AbstractLevelDOWN and leave it to the back-end to decide whether to implement & expose it. Ultimately I'd like to see approximateSize gone from LevelUP, although we can leave the documentation telling how to access it with db.db.approximateSize().
Perhaps we should accelerate this for the next LevelUP release and then your feature-detection could just involve checking for db.db.approximateSize.

[Raynos]

is db.db a thing? its that levelUpDbInstance.abstractLevelDownDbInstance ?

[rvagg]

yeah, each LevelUP instance has a 'db' property that points to the underlying store, usually an instance of LevelDOWN but it'll be whatever was created when you pass in the 'db' property on init. The idea is to be able to expose store-specific functionality, like approximateSize() and probably createSnapshot(). LMDB would get something like createTransaction() perhaps, these things don't belong in LevelUP.

[mcollina]

@rvagg I can't agree more with you that approximateSize should be gone from LevelUp, and just detecting if db.db.approximateSize exist is nice. Let me know how I can help you.

[vweevers]

Ref Level/deferred-leveldown#35.

[vweevers]

Absorbing into Level/community#83.