Detect whether a font is bold/italic on iOS?

Question

Given a UIFont or a CTFont, how can I tell whether the font is bold/italic?

Answer 1

Answer for Swift 3/4 based on Arjan's answer:

extension UIFont {
    var isBold: Bool {
        return fontDescriptor.symbolicTraits.contains(.traitBold)
    }

    var isItalic: Bool {
        return fontDescriptor.symbolicTraits.contains(.traitItalic)
    }
}