问奇怪的XCode 7接口生成器警告

EN

import AppKit

@IBDesignable public class TextField: NSTextField
{
    @IBInspectable public var preferredFontWeight: Int = 0

    override public func awakeFromNib() {
        if #available(OSX 10.11, *) {
            return
        }

        guard
        let weight: Int = self.preferredFontWeight where weight > 0,
        let font: NSFont = self.font,
        let name: String = font.familyName,
        let manager: NSFontManager = NSFontManager.sharedFontManager() else {
            return
        }


        // Full details here – https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Classes/NSFontManager_Class/#//apple_ref/occ/instm/NSFontManager/convertWeight:ofFont:   
        //
        // 1 – ultralight
        // 2 – thin
        // 3 – light, extralight
        // 4 – book
        // 5 – regular, display
        // 6 – medium
        // 7 – demi, demibold
        // 8 – semi, semibold
        // 9 – bold
        // 10 – extra, extrabold
        // 11 – heavy
        // 12 – black
        // 13 – ultrablack
        // 14 – extrablack

        if let font: NSFont = manager.fontWithFamily(name, traits: manager.traitsOfFont(font), weight: weight, size: font.pointSize) {
            self.font = font
        }
    }
}