Animated assign subscriber

[icanzilb]

This PR adds a variation of assign(to:on:) with an extra parameter allowing the user to set an animation transition to play when emitting output values.

E.g. if you have:

let counts = ["One", "Two", "Three", "Four", "Five"]

Timer.publish(every: 1, on: RunLoop.main, in: .common)
    .autoconnect()
    .scan(0) { (result, _) -> Int in
        return result + 1 >= counts.count ? 0 : result + 1
    }
    .map { counts[$0] }
    .assign(to: \UILabel.text, on: label, animation: .flip(direction: .left, duration: 0.25))
    .store(in: &subscriptions)

It makes the updates to the label animated like so:

[freak4pc]

Looks great! Have a few quick notes here :)

[icanzilb]

Thanks @freak4pc - merged and removed the guard too.

[freak4pc]

Sorry for the delay here, crazy few days. Noticed two more quick notes that I wanted to ask you about.

[freak4pc]

Not sure why this looks misaligned... tabs and spaces together?

[freak4pc]

Another question that popped to my head,
You're already setting the value inside the animation block, and the assign will do so again.

Maybe it's worth swapping the assign with something like sink(receiveValue: { _ in }). Just to active the chain? (same for below)

[freak4pc]

Hey @icanzilb - any chance you have a moment to answer above questions? Happy to help carry this over the merge line with you

[icanzilb]

@freak4pc yikes, it seems I missed this one - looking at it this afternoon 👍🏼

[icanzilb]

@freak4pc 👆🏼

[freak4pc]

Yikes, was sure I already merged this.
Sorry @icanzilb ! Looks good.