@IBInspectable in Swift 4.0

While migrating to Swift 4.0, I am facing an issue with @IBInspectable,

open class SVContactBubbleView: UIView 
{
   @IBInspectable open var dataSource: SVContactBubbleDataSource? //ERROR..!!
   @IBInspectable open var delegate: SVContactBubbleDelegate? //ERROR..!!
}

public protocol SVContactBubbleDataSource
{
    //Methods here
}

public protocol SVContactBubbleDelegate
{
    //Methods here
}

The error that appears is:

Property cannot be marked @IBInspectable because its type cannot be represented in Objective-C

In Swift 3, it was working fine. I don't understand what went wrong in Swift 4.

Also, the compiler is not showing any suggestion. It just shows an error message.

Add notation @objc for both delegate and datasource in Swift 4 (as shown in below code)

open class SVContactBubbleView: UIView {
    @IBInspectable open var dataSource: SVContactBubbleDataSource? 
    @IBInspectable open var delegate: SVContactBubbleDelegate? 
}

@objc  // add notation here
public protocol SVContactBubbleDataSource
{
    //Methods here
}


@objc  // add notation here
public protocol SVContactBubbleDelegate
{
    //Methods here
}

Here is ref. snapshot with error resolution:

Here is Apple document for @objc notation - Protocol - Optional Protocol Requirements