How can I pass a function a parameter

It is not alwaysa great idea to try to cram everything in a single line…

Anyway, texture parameter is a SKTexture, not a func nor a closure.

But there is a simple way to achieve your goal:

Code Block 
let mySlot = SKSpriteNode(texture: SKTexture(imageNamed: "slot"), color: .clear, size: slotSize)

If the closure is something that I must predefine, then there's no point in trying this.

Seems the answer of Claud31's is best fit for your purpose.

If you dare use closures, you can predefine a initializer using closure:

Code Block 
extension SKSpriteNode {
    convenience init(color: UIColor, size: CGSize, texture closure: ()->SKTexture) {
        self.init(texture: closure(), color: color, size: size)
    }
}

And use it like this:

Code Block 
        let mSlot = SKSpriteNode(color: SKColor.clear, size: mySlotSize) {
            return SKTexture(imageNamed: "slot")
        }

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Or else, you can invoke a closure instantly at the place, as often found in the initial values of properties:

Code Block 
        let mSlot = SKSpriteNode(texture: {
            return SKTexture(imageNamed: "slot")
        }(), color: SKColor.clear, size: mySlotSize)

This make your code more complex than it should be, so may not the thing you want to achieve.

(You can omit the keyword return in both cases, but I made them left there as to clarify they are in closures.)

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Maybe we are misunderstanding what you really want to do. If you could clarify that, there might be some other ways.