Set and Map support for _.isEmpty

[ushakov-igor]

Added support for Set and Map for _.isEmpty

[patseev]

That's a nice idea. Used to write my own wrapper for this functionality

[jgonggrijp]

@ushakov-igor Thank you for taking the effort to submit a pull request.

I think this would be nice to have, but it is a breaking change, so we have to be careful. Your PR may remain open for a while because of this.

For consistency, it would be best if all collection functions would treat Map and Set in the same way. This is not necessarily a bad idea, but it does make this a rather big breaking change.

I also recently learned from #2840 that the toString-based type checks like isMap are relatively slow. So to avoid a big slowdown in all functions that support Map and Set, there would have to be an isAssociative fuzzy checker analogous to the internal isArrayLike. I imagine the implementation might go like this:

var getSize = shallowProperty('size');
var getForEach = shallowProperty('forEach');

function isAssociative(collection) {
    var size = getSize(collection);
    var forEach = getForEach(collection);
    return typeof size == 'number' && typeof forEach == 'function' && size >= 0 && size <= MAX_ARRAY_INDEX;
}

[jashkenas]

For consistency, it would be best if all collection functions would treat Map and Set in the same way. This is not necessarily a bad idea, but it does make this a rather big breaking change.

Agreed. If we’re going to support Maps and Sets (and WeakMaps and WeakSets?), we should do it across the board, in a single release, and not piecemeal function-by-function.

[jgonggrijp]

WeakMaps and WeakSets cannot be iterated, so I don't think there's much to support about them in collection functions.