I am thinking you don't know the difference between a Function and a Method. Here:

1) FUNCTION

struct NeededParams {

var x: Float

var y: Float

}

func doSomethingWith(x: Float, y: Float) -> NeededParams {

let result: NeededParams(x: x*x, y: y*y)

return result

// did something

}

let someParameters: NeededParams = doSomething(x: 3, y: 4)

–––––––––––––––

2) METHOD

var triangleLength: Float = 0.0

@objc

func perfomSomething(_ parameters: NeededParams) {

triangleLength = sqrt(parameters.x + parameters.y)

// performs something

}

The you use: someClassInstance.perform(Selector(performSomething), with: someParameters)

That's the difference between a Swift Function and a Swift Method.

Geesh