Interpolated Visual Constraint Language

ConstraintBuilder.swift

// Example

let blueView = UIView()
blueView.backgroundColor = UIColor.blueColor()
blueView.translatesAutoresizingMaskIntoConstraints = false

let greenView = UIView()
greenView.backgroundColor = UIColor.greenColor()
greenView.translatesAutoresizingMaskIntoConstraints = false

let redView = UIView()
redView.backgroundColor = UIColor.redColor()
redView.translatesAutoresizingMaskIntoConstraints = false

view.addSubview(blueView)
view.addSubview(greenView)
view.addSubview(redView)

let size = 60
view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("|-[\(blueView)(\(size))]-[\(redView)(==\(greenView))]-[\(greenView)(==\(redView))]-|"))
view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-[\(redView)(\(size))]-[\(greenView)(==\(blueView))]-[\(blueView)(==\(greenView))]-|"))

// BAM! https://pbs.twimg.com/media/CIaWFfqUMAE307B.png:large

// Implementation

struct ConstraintBuilder : StringInterpolationConvertible {
    let format: String
    let metrics: [String : NSNumber]
    let views: [String : UIView]
    
    init(stringInterpolation strings: ConstraintBuilder...) {
        format = "".join(strings.map{ $0.format })
        metrics = strings.map{ $0.metrics }.reduce([String : NSNumber]()){ $0 + $1 }
        views = strings.map{ $0.views }.reduce([String : UIView]()){ $0 + $1 }
    }
    
    init<T>(stringInterpolationSegment expr: T) {
        format = "\(expr)"
        metrics = [String : NSNumber]()
        views = [String : UIView]()
    }
    
    init(stringInterpolationSegment expr: UIView) {
        format = uniqueName(expr)
        metrics = [String : NSNumber]()
        views = [format : expr]
    }
    
    init(stringInterpolationSegment expr: NSNumber) {
        format = expr.stringValue
        metrics = [format : expr]
        views = [String : UIView]()
    }
}

extension NSLayoutConstraint {
    static func constraintsWithVisualFormat(builder: ConstraintBuilder, options: NSLayoutFormatOptions = []) -> [NSLayoutConstraint] {
        return constraintsWithVisualFormat(builder.format, options: options, metrics: builder.metrics, views: builder.views)
    }
}

// Helpers

func memoryAddress(object: AnyObject) -> String {
    return Unmanaged.passUnretained(object).toOpaque().debugDescription
}

func uniqueName(object: AnyObject) -> String {
    return String(memoryAddress(object).characters.map { char in
        switch char {
        case "0": return "A"
        case "1": return "B"
        case "2": return "C"
        case "3": return "D"
        case "4": return "E"
        case "5": return "F"
        case "6": return "G"
        case "7": return "H"
        case "8": return "I"
        case "9": return "J"
        default: return char
        }
    })
}

func +<K,V>(var lhs: Dictionary<K,V>, rhs: Dictionary<K,V>) -> Dictionary<K,V> {
    for (key, value) in rhs {
        lhs.updateValue(value, forKey: key)
    }
    return lhs
}