How to add OR condition in Swift generic where clause?

Question

I am extending SCNVector3 from Apple SceneKit with arithmetic operations with a number. I use generic for the number's type, but I have found out that I have to write at least two versions of each function, as this does not work:

extension SCNVector3 {
    static func *<T> (left: SCNVector3, right: T) -> SCNVector3 {
        return SCNVector3(left.x * Float(right), left.y * Float(right), left.z * Float(right))
}

and gives error Cannot invoke initializer for Type 'Float' with an argument list of type '(T)'

Looking at definition of Float in Apple documentation, I see that the most generic I can get is init<Source: BinaryFloatingPoint> or init<Source: BinaryInteger>.

So I have to rewrite the extension as following, making two almost identical functions for each operation:

extension SCNVector3 {
    static func *<T> (left: SCNVector3, right: T) -> SCNVector3 where T: BinaryFloatingPoint {
        return SCNVector3(left.x * Float(right), left.y * Float(right), left.z * Float(right))

    static func *<T> (left: SCNVector3, right: T) -> SCNVector3 where T: BinaryInteger {
        return SCNVector3(left.x * Float(right), left.y * Float(right), left.z * Float(right))
}

I can place AND in where clause — by having two conditions after where separated by a comma.

But is there any way I can place OR there?

Answer 1

Your basic implementation should start by this:

extension SCNVector3 {
    static func * (vector: SCNVector3, scale: Float) -> SCNVector3 {
        return SCNVector3(vector.x * scale, vector.y * scale, vector.z * scale)
    }
}

The vector has Float components therefore you should always multiplicate only by a Float. That's how all operators in Swift work. If you have a different type, cast it before multiplicating, not as a side-effect of multiplication.

If you really want to pass other types, then you can use method overloading:

extension SCNVector3 {
    static func *<T> (left: SCNVector3, right: T) -> SCNVector3 where T: BinaryFloatingPoint {
        return left * Float(right)
    }

    static func *<T> (left: SCNVector3, right: T) -> SCNVector3 where T: BinaryInteger {
        return left * Float(right)
    }
}

There is no way how to define or in types.