Set global font for iOS app in one place

Fonts.swift

// MARK: - Swizzling
extension UIFont {
  class var defaultFontFamily: String { return "Georgia" }
  
  override public class func initialize()
  {
    if self == UIFont.self {
      swizzleSystemFont()
    }
  }
  
  private class func swizzleSystemFont()
  {
    let systemPreferredFontMethod = class_getClassMethod(self, "preferredFontForTextStyle:")
    let mySystemPreferredFontMethod = class_getClassMethod(self, "myPreferredFontForTextStyle:")
    method_exchangeImplementations(systemPreferredFontMethod, mySystemPreferredFontMethod)
    
    let systemFontMethod = class_getClassMethod(self, "systemFontOfSize:")
    let mySystemFontMethod = class_getClassMethod(self, "mySystemFontOfSize:")
    method_exchangeImplementations(systemFontMethod, mySystemFontMethod)
    
    let boldSystemFontMethod = class_getClassMethod(self, "boldSystemFontOfSize:")
    let myBoldSystemFontMethod = class_getClassMethod(self, "myBoldSystemFontOfSize:")
    method_exchangeImplementations(boldSystemFontMethod, myBoldSystemFontMethod)
    
    let italicSystemFontMethod = class_getClassMethod(self, "italicSystemFontOfSize:")
    let myItalicSystemFontMethod = class_getClassMethod(self, "myItalicSystemFontOfSize:")
    method_exchangeImplementations(italicSystemFontMethod, myItalicSystemFontMethod)
  }
}

// MARK: - New Font Methods
extension UIFont {
  private class func myPreferredFontForTextStyle(style: String) -> UIFont
  {
    let defaultFont = myPreferredFontForTextStyle(style)  // will not cause stack overflow - this is now the old, default UIFont.preferredFontForTextStyle
    let newDescriptor = defaultFont.fontDescriptor().fontDescriptorWithFamily(defaultFontFamily)
    return UIFont(descriptor: newDescriptor, size: defaultFont.pointSize)
  }
  
  private class func mySystemFontOfSize(fontSize: CGFloat) -> UIFont
  {
    return myDefaultFontOfSize(fontSize)
  }
  
  private class func myBoldSystemFontOfSize(fontSize: CGFloat) -> UIFont
  {
    return myDefaultFontOfSize(fontSize, withTraits: .TraitBold)
  }
  
  private class func myItalicSystemFontOfSize(fontSize: CGFloat) -> UIFont
  {
    return myDefaultFontOfSize(fontSize, withTraits: .TraitItalic)
  }
  
  private class func myDefaultFontOfSize(fontSize: CGFloat, withTraits traits: UIFontDescriptorSymbolicTraits = []) -> UIFont
  {
    let descriptor = UIFontDescriptor(name: defaultFontFamily, size: fontSize).fontDescriptorWithSymbolicTraits(traits)
    return UIFont(descriptor: descriptor, size: fontSize)
  }
}