Switch Latest without Ramda Dependency

[NoelAbrahams]

Hi

Is there a simple way to replace ramda/drop in the following without breaking anything?

var flyd = require('../../lib');
var takeUntil = require('../takeuntil');
var drop = require('ramda/src/drop');

var dropCurrentValue = flyd.transduce(drop(1));

module.exports = function(s) {
  return flyd.combine(function(stream$, self) {
    var value$ = stream$();
    flyd.on(self, takeUntil(value$, dropCurrentValue(stream$)));
  }, [s]);
};

This is the only module that I've run into so far with an external dependency, which I'd like to avoid if possible. Any help would be much appreciated. Thanks

[nordfjord]

Should be possible to implement it as

function dropCurrentValue(s) {
  var dropped = false
  return flyd.combine(function(stream$, self) {
    if (!dropped) {
      dropped = true
      return
    }
    self(stream$.val)
  }, [s])
}

[NoelAbrahams]

Ah, thanks @nordfjord. You have literally saved me 100 LOC after my attempt to rework this!

I've also tried to convert this to switchMap:

flyd.switchMap = projector => stream => switchLatest(flyd.map(projector, stream));

For usage in pipe, like this:

const stream = flyd.stream<number>();
stream.pipe(
    flyd.switchMap(value => flyd.stream(value * 10)))
    .map(value => {
        console.error(value); // '10'
    });

stream(1);

I'm about 90% sure that's not the way to define switchMap?!

[nordfjord]

Did you write a small suite of tests to ensure it does what you want it to? 😜

[NoelAbrahams]

Haha. Test cases are for losers.

But actually you do me an injustice. It's quite well tested. It's currently doing what I want it to do. But I have concerns that it won't conform to how the other modules are defined. I'm using it in pipe as above, but I also notice that some modules allow the stream to be passed in. TBH the modules don't really seem to be very consistent.

[nordfjord]

FWIW I think that’s a fine implementation of switchMap, simple composition goes a long way.

as for the consistency of modules, yes, agreed

[NoelAbrahams]

Thanks for the sanity check @nordfjord. Appreciate your help with this.