.diff / .scan / .reduce without seed (need help with names for new methods) about kefir HOT 9 CLOSED

Another approach would be to swap seed and fn arguments so it will be .diff(fn, seed) instead of .diff(seed, fn). Then it will become clear which argument is omitted:

• diff(a) — seed omitted
• diff(null, a) — fn omitted
• diff() — both

But it's a breaking change ...

from kefir.

Another approach would be to swap seed and fn arguments so it will be .diff(fn, seed) instead of .diff(seed, fn).

These sounds like proper way. Same order as in Array.prototype.reduce.

BTW how about diff(seed, fn), diff(seed), diff() and diffByFunction(fn) (or simply diffBy(fn))?

from kefir.

Yeah, I am also thinking of doing swapping.
But not sure about diffByFunction / diffBy, diff(null, a) is good enough.

from kefir.

Kefir uses semver so nothing stops you to make breaking changes in next major version.
Also something like diff(_.noop, seed) looks much better then diff(null, seed) I think. But there is another issue when you really need to return undefined value in diff function.

from kefir.

Now I think diff(null, seed) is ok. As it in Node.js callback error conventions and in some other libraries.

Just noticed, documentation says that

If no fn function provided, function(a, b) {return [a, b]} will be used as default.

Why not just identity function of new value?
Also I believe that swapped order (i.e. function (next, prev) { /* ... */}) is more traditional. Diffs algorithms in all major libraries and frameworks use that order. In this way you can just omit old value in callback function if you don't need it.

from kefir.

Now I think diff(null, seed) is ok

Yes, we can't use _.noop, because it will result in observable always emitting undefined (which _.noop always return).

Why not just identity function of new value?

If function(a, b) {return b} was used, then a.diff(seed) would be equivalent of just a.

from kefir.

Yes, we can't use _.noop, because it will result in observable always emitting undefined (which _.noop always return).

But I mean diff(_.noop, seed) not diff(_.noop(), seed). _.noop itself is not undefined but function so it'll be used as diff function returning null.

If function(a, b) {return b} was used, then a.diff(seed) would be equivalent of just a.

That makes sense.

from kefir.

so it'll be used as diff function returning null

yep, and that null will be emitted from result observable. That what I am trying to say)

from kefir.

oh I just hasn't realized that we are speaking about same things sorry

from kefir.