Spread variable parameter count on generic function - swift

Question

In javascript it is pretty easy to take a variable count of arguments and pass it to a sub function without the need to modify the sub function. For example, you want to write a wrapper function which takes a generic function as first argument and calls it with the rest of the arguments:
function wrapper(func, ...args) {
return func(...args)
}
I want to archive something similar in swift. There I have many many c function which I want to wrap with another function for some safety reasons.
Now I have two major road blockers:
The first one: I don't know how to do something like func(...args) in swift. This is why I temporary tried this:
private func apply<ReturnValue, FunctionParams>(_ fun: (_ params: FunctionParams...) -> ReturnValue, _ paramsPass: [FunctionParams]) throws -> ReturnValue {
switch paramsPass.count {
case 0:
return fun()
case 1:
return fun(paramsPass[0])
case 2:
return fun(paramsPass[0], paramsPass[1])
case 3:
return fun(paramsPass[0], paramsPass[1], paramsPass[2])
case 4:
return fun(paramsPass[0], paramsPass[1], paramsPass[2], paramsPass[3])
case 5:
return fun(paramsPass[0], paramsPass[1], paramsPass[2], paramsPass[3], paramsPass[4])
case 6:
return fun(paramsPass[0], paramsPass[1], paramsPass[2], paramsPass[3], paramsPass[4], paramsPass[5])
default:
throw NSError(domain: "apply", code: paramsPass.count, userInfo: nil);
}
}
This is not really good and only works for a max parameter count of 6.
The second road blocker is, I am not able to write the required swift types to archive something like I described. This is what I tried:
private func runUnsafeFunction<ReturnValue, FunctionParams>(_ fun: (_ params: FunctionParams...) -> ReturnValue, _ paramsPass: FunctionParams...) throws -> ReturnValue {
// wrapper code
return try apply(fun, paramsPass)
}
However, if I try to call it, I get: Generic parameter 'ReturnValue' could not be inferred
Probably I miss something here. But at this point I am stuck.

Answer 1

Why not pass the function and its arguments in a closure?
func runUnsafeFunction<ReturnValue>(function: () -> ReturnValue) -> ReturnValue {
// do stuff
return function()
}
Example
func add(_ a: Int, _ b: Int) -> Int {
a + b
}
func add(_ a: Int, _ b: Int, _ c: Int) -> Int {
a + b + c
}
let result = runUnsafeFunction { add(3, 4) }
let result2 = runUnsafeFunction { add(3, 4, 5) }