Overload NSLayoutConstraint.activate to Accept Arrays as Elements

Using anchors with Auto Layout is a big improvement over creating constraints using the class function in NSLayoutConstraint or Visual Format Language. I don’t use Interface Builder so I write all my layout in code. You also write your own wrappers to make creating multiple constraints easier, e.g one might write a function like NSLayoutConstraint.constraint(views:toSameWidth:) or NSLayoutConstraint.constraint(views:toSquareWithSides:), both returning an array.

Or sometimes, in a more dynamic piece of UI, you might need to swap around arrays of constraints.

I find it useful to define a protocol and a few extensions so that this can be done:

NSLayoutConstraint.activate([
    constraintsArray1,
    constraintsArray2,
    constraint3,
    constraint4,
    constraint5,
])

Alternatives involve appending of arrays which ends up with code that is hard to indent.

So there you go:

protocol LayoutConstraintsWrapper {
    var constraints: [NSLayoutConstraint] { get }
}

extension Array: LayoutConstraintsWrapper where Element: NSLayoutConstraint {
    var constraints: [NSLayoutConstraint] {
        return self
    }
}

extension NSLayoutConstraint: LayoutConstraintsWrapper {
    var constraints: [NSLayoutConstraint] {
        return [self]
    }
}

extension NSLayoutConstraint {
    class func activate(_ constraints: [LayoutConstraintsWrapper]) {
        activate(constraints.flatMap { $0.constraints })
    }
}