swift label only border left

Swift 3 version:

extension CALayer {

    func addBorder(edge: UIRectEdge, color: UIColor, thickness: CGFloat) {

        let border = CALayer()

        switch edge {
        case UIRectEdge.top:
            border.frame = CGRect(x: 0, y: 0, width: self.frame.width, height: thickness)
            break
        case UIRectEdge.bottom:
            border.frame = CGRect(x: 0, y: self.frame.height - thickness, width: self.frame.width, height: thickness)
            break
        case UIRectEdge.left:
            border.frame = CGRect(x: 0, y: 0, width: thickness, height: self.frame.height)
            break
        case UIRectEdge.right:
            border.frame = CGRect(x: self.frame.width - thickness, y: 0, width: thickness, height: self.frame.height)
            break
        default:
            break
        }

        border.backgroundColor = color.cgColor;

        self.addSublayer(border)
    }

}

Or use IBDesignable (see answer below)

Swift 4 Version:

extension CALayer {
    func addBorder(edge: UIRectEdge, color: UIColor, thickness: CGFloat) {

        let border = CALayer()

        switch edge {
            case UIRectEdge.top:
             border.frame = CGRect(x: 0, y: 0, width: self.bounds.width, height: thickness)

            case UIRectEdge.bottom:
             border.frame = CGRect(x: 0, y: self.bounds.height - thickness,  width: self.bounds.width, height: thickness)

            case UIRectEdge.left:
             border.frame = CGRect(x: 0, y: 0,  width: thickness, height: self.bounds.height)

            case UIRectEdge.right:
             border.frame = CGRect(x: self.bounds.width - thickness, y: 0,  width: thickness, height: self.bounds.height)

            default:
             break
        }
        border.backgroundColor = color.cgColor;
        self.addSublayer(border)
    }
}

Here is an extension you can add to your project:

extension CALayer {

    func addBorder(edge: UIRectEdge, color: UIColor, thickness: CGFloat) {

        var border = CALayer()

        switch edge {
        case UIRectEdge.Top:
            border.frame = CGRectMake(0, 0, CGRectGetHeight(self.frame), thickness)
            break
        case UIRectEdge.Bottom:
            border.frame = CGRectMake(0, CGRectGetHeight(self.frame) - thickness, UIScreen.mainScreen().bounds.width, thickness)
            break
        case UIRectEdge.Left:
            border.frame = CGRectMake(0, 0, thickness, CGRectGetHeight(self.frame))
            break
        case UIRectEdge.Right:
            border.frame = CGRectMake(CGRectGetWidth(self.frame) - thickness, 0, thickness, CGRectGetHeight(self.frame))
            break
        default:
            break
        }

        border.backgroundColor = color.CGColor;

        self.addSublayer(border)
    }

}

And the use it like this:

cell.Label.layer.addBorder(UIRectEdge.Top, color: UIColor.greenColor(), thickness: 0.5)

FOR SWIFT 3, 4 & 5:

extension CALayer {

    func addBorder(edge: UIRectEdge, color: UIColor, thickness: CGFloat) {

        let border = CALayer()

        switch edge {
        case UIRectEdge.top:
            border.frame = CGRect(x: 0, y: 0, width: self.frame.height, height: thickness)
            break
        case UIRectEdge.bottom:
            border.frame = CGRect(x: 0, y: self.frame.height - thickness, width: UIScreen.main.bounds.width, height: thickness)
            break
        case UIRectEdge.left:
            border.frame = CGRect(x: 0, y: 0, width: thickness, height: self.frame.height)
            break
        case UIRectEdge.right:
            border.frame = CGRect(x: self.frame.width - thickness, y: 0, width: thickness, height: self.frame.height)
            break
        default:
            break
        }

        border.backgroundColor = color.cgColor;

        self.addSublayer(border)
    }

}