Trouble using callbacks with CGPattern in Swift3

I'm attempting to create a colored pattern using CGPattern in Swift. Apple provides a nice Objective-C example in the Quartz 2D Programming Guide in their section on Painting Colored Patterns. But getting all of that syntax converted from Objective-C is not straight forward. Plus I'd like to make use of the info parameter in the drawing callback and there is no example of doing that.

Here's my first attempt:

class SomeShape {
    func createPattern() -> CGPattern? {
        let bounds = CGRect(x: 0, y: 0, width: someWidth, height: someHeight)
        let matrix = CGAffineTransform.identity
        var callbacks = CGPatternCallbacks(version: 0, drawPattern: nil, releaseInfo: nil)

        let res = CGPattern(info: nil, bounds: bounds, matrix: matrix, xStep: bounds.width, yStep: bounds.height, tiling: .noDistortion, isColored: true, callbacks: &callbacks)

        return res
    }
}

Clearly this needs a proper value for the drawPattern parameter to CGPatternCallbacks and I need to pass self as the info parameter to the CGPattern initializer.

What is the proper syntax to complete this?