CustomStringConvertible for optionals

Hi there.

I am trying to have a default string interpolation for optionals to be able to use it like

let foo: Float? = 3.4
print("foo \(foo)") // "3.4"
let bar: Float? = nil
print("bar \(bar)") // "-"

I wrote

extension Optional: CustomStringConvertible where Wrapped: CustomStringConvertible {
  public var description: String {
    self?.description ?? "-"

But this will print "No exact matches in call to instance method 'appendInterpolation'" for "\(foo)".

However, I can do "\(foo.description)", which works fine.

I guess the issue is that the compiler does not realize that the optional type is actually conforming to "CustomStringConvertible".

Is there a way to fix this?

Just out of curiosity, as I think this solution is actually better.