Is there a way to convert any generic Numeric into a Double?

Question

So I have a method that has 3 different types of arguments that could come in:

Int32, Int and Double. So the idea was to use

Answer 1

... because there is no initializer for Double that takes a Generic.

That is not entirely true. There is no initializer taking a Numeric argument. But there are generic initializers taking BinaryInteger and BinaryFloatingPoint arguments, so that two overloads are sufficient:

func resetProgressBarChunks(originalIterationCount: T) {
    let iCount = Double(originalIterationCount)
    // ...
}

func resetProgressBarChunks(originalIterationCount: T) {
    let iCount = Double(originalIterationCount)
    // ...
}

This covers Double, Int, Int32 arguments as well as Float and all other fixed-size integer types.