wrapCallback and callbacks with more than two arguments

[d4h0]

Hi,

Why does wrapCallback ignore the third argument if there is one?

Wouldn't it be easy to check if there are more than two arguments and if so to put an array of these arguments into the stream?

Best regards,
Daniel

[apaleslimghost]

I agree that it would be good to support callbacks with multiple parameters, and it's easy enough to implement, but I think it feels a bit weird to emit single values in some cases and arrays in others. We might end up in a case where a callback is called with a different number of arguments at different times, and that would get hard to abstract over.

Perhaps a wrapCallbackN would work? You'd pass it a function and expected number of arguments and it would always emit an array of that length. Something like:

_.wrapCallbackN = function(fn, n) {
  return _.wrapCallback(function(...args, cb) {
    fn(...args, function(e, ...results) {
      cb(e, ensureArrayLength(n, results));
    });
  });
}

(Note that, unlike other cases such as uniq/uniqBy, wrapCallbackN(_, 1) would not be equivalent to wrapCallback)

[d4h0]

Isn't this the same problem that the EventEmitter Stream constructor had?

Maybe that code can be reused?

[apaleslimghost]

Ah, good find. Adding mappingHint to wrapCallback is a good idea, I'll send a pull request in a bit.

p.s. We usually avoid optional parameters, because they don't work with currying, but since this is a constructor function, not a stream method, that doesn't apply here (unless anyone disagrees!)

[apaleslimghost]

⇒ #247

[d4h0]

Thanks, @quarterto!

[vqvu]

Reopening until #247 is merged.

[dypsilon]

Please consider solving #334 with mappingHint.

[vqvu]

@quarterto, you you have time to finish up #247?

[apaleslimghost]

Wow, sorry, that totally slipped off my radar. I'll have a look this afternoon.