Optional location

[ralphtheninja]

Closes https://github.com/Level/abstract-leveldown/issues/63

[ralphtheninja]

Rebased onto latest master. Needs docs too I guess.

[vweevers]

Can you add a note to UPGRADING.md? We'll need to add type checks to leveldown etc

[ralphtheninja]

Browser tests never started, restarting build.

[vweevers]

Entertaining two thoughts, because I think we can afford to take bigger steps.

Thought 1. Make location optional by checking arguments.length. This gives implementations the choice of supporting location without them having to do extra type checks. In addition, make the .location property optional too?

function AbstractLevelDOWN (location) {
  if (arguments.length > 0) {
    if (typeof location !== 'string') {
      throw new Error('constructor requires a location string argument')
    }

    this.location = location
  }

  this.status = 'new'
}

function MemDOWN () {
   AbstractLevelDOWN.call(this)
}

function LevelDOWN (location) {
  AbstractLevelDOWN.call(this, location)
}

function SQLDown (connection) {
  this._connection = connection
  AbstractLevelDOWN.call(this)
}

Thought 2. Remove location altogether, it's not that much code to move to leveldown:

function AbstractLevelDOWN () {
  this.status = 'new'
}

function MemDOWN () {
   AbstractLevelDOWN.call(this)
}

function LevelDOWN (location) {
  if (typeof location !== 'string') {
    throw new Error('constructor requires a location string argument')
  }

  this._location = location
  AbstractLevelDOWN.call(this)
}

function SQLDown (connection) {
  this._connection = connection
  AbstractLevelDOWN.call(this)
}

An additional benefit of either of these approaches is that we can check location !== ''. Are empty locations handled in the c++?

[ralphtheninja]

Entertaining two thoughts, because I think we can afford to take bigger steps.

Good call!

I like both alternatives, but I think I prefer the second. Since some implementation aren't using location I don't see why it should be stored in a base class at all. Also makes AbstractLevelDOWN a lot cleaner.

[ralphtheninja]

Additionally, I think we might need to change how the abstract tests are invoked as well. If location is removed from abstract-leveldown and if implementations aren't necessarily using a location, then maybe we shouldn't do e.g.

var db = leveldown(testCommon.location())

but rather

var db = factory()

So implementations pass in factory instead and can handle themselves how the instance should be created, with a location or not.

[ralphtheninja]

Aaah we're of course already using a factory, so we shouldn't pass testCommon.location() to it.

[vweevers]

A factory can also support options (#227). Two birds one stone :)

[vweevers]

Aaah we're of course already using a factory

So none of the current tests assume that the function has a prototype?

[ralphtheninja]

So none of the current tests assume that the function has a prototype?

I haven't checked all. With that you mean that we don't have to call new?

[vweevers]

With that you mean that we don't have to call new?

And that the tests don't do things like instanceof fn

[ralphtheninja]

@vweevers If you're cool with it, I'd like to close this PR and start over with removing location.

Ps. It seems to me that test/leveldown-test.js is getting more and more redundant since it will be only one test left which doesn't really test anything

https://github.com/Level/abstract-leveldown/blob/74d7340dbf85ceae4f69f7bc9ea9d541498c3a8d/test/leveldown-test.js#L21-L26