CGRect extension gets and sets a rectangle's corners

gistfile1.txt

extension CGRect
{
    
    /// Return corners in order of top left, top right, bottom left, bottom right
    var corners: [CGPoint]
    {
        return [
            CGPoint(x: minX, y: minY),
            CGPoint(x: maxX, y: minY),
            CGPoint(x: minX, y: maxY),
            CGPoint(x: maxX, y: maxY)
        ]
    }
    
    /// Sets corner position at given index based on `corners`
    mutating func setCornerAtIndex(index: Int, position: CGPoint)
    {
        switch index
        {
        case 0:
            size.width = size.width + (origin.x - position.x)
            size.height = size.height + (origin.y - position.y)
            
            origin.x = position.x
            origin.y = position.y
            
        case 1:
            size.width = position.x - origin.x
            size.height = size.height + (origin.y - position.y)
            
            origin.y = position.y
            
        case 2:
            size.width = size.width + (origin.x - position.x)
            size.height = position.y - origin.y
            
            origin.x = position.x
            
        case 3:
            size.width = position.x - origin.x
            size.height = position.y - origin.y
            
        default:
            break
        }
    }
}