Example of switch contains.

ContainmentMatcher.swift

// Code via Olivier Halligon and Nate Cook

struct ContainmentMatcher<T: Hashable> {
    let set: Set<T>
    
    static func ~=(lhs: ContainmentMatcher<T>, rhs: Set<T>) -> Bool {
        return rhs.isSuperset(of: lhs.set)
    }
}

func contains<T>(_ set: Set<T>) -> ContainmentMatcher<T> {
    return ContainmentMatcher(set: set)
}

Pin.swift

// ..part of a larger thing..

/// Pin item to the sides of the parent or reference item with optional insets.
/// Specifying opposing sides will flex width/height.
func pin(to sides:Layout.Sides, with insets:InsetGroup) {
    
    // ..
    
    let topInset        = insets.value(for: .top)
    let bottomInset     = insets.value(for: .bottom)
    let leadingInset    = insets.value(for: .leading)
    let trailingInset   = insets.value(for: .trailing)
    
    var x:CGFloat!      = item.frame.origin.x
    var y:CGFloat!      = item.frame.origin.y
    var width:CGFloat!  = item.frame.width
    var height:CGFloat! = item.frame.height
    
    let _edges = Set(sides.edges)
    
    switch _edges {
    case contains([.top, .bottom]) :
        // pin top and bottom, flex height
        y = topInset
        height = referenceBounds.height - topInset - bottomInset
    case contains([.top]) :
        // pin top, maintain height
        y = topInset
    case contains([.bottom]) :
        // pin bottom, maintain height
        y = referenceBounds.height - height - bottomInset
    default : break
    }
    
    switch _edges { // TODO support layout direction flip
    case contains([.leading, .trailing]) :
        // pin leading/trailing, flex width
        x = leadingInset
        width = referenceBounds.width - leadingInset - trailingInset
    case contains([.leading]) :
        // pin leading, maintain width
        x = leadingInset
    case contains([.trailing]) :
        // pin trailing, maintain width
        x = referenceBounds.width - width - trailingInset
    default : break
    }
    
    let newFrame = CGRect(x:x, y:y, width:width, height:height)
    
    // .. update frame
    
    // ..
}