UIFont extensions to be able to get bold and bold italic fonts directly from a UIFont object

UIFont+.swift

/**
 Swift 2
 UIFont extensions to be able to get bold and bold italic fonts directly
 from a UIFont object
 */
import Foundation
import UIKit

extension UIFont {
    
    func withTraits(traits:UIFontDescriptorSymbolicTraits...) -> UIFont {
        let descriptor = self.fontDescriptor()
            .fontDescriptorWithSymbolicTraits(UIFontDescriptorSymbolicTraits(traits))
        return UIFont(descriptor: descriptor, size: 0)
    }
    
    func boldItalic() -> UIFont {
        return withTraits(.TraitBold, .TraitCondensed)
    }
    
    func bold() -> UIFont {
        return withTraits(.TraitBold)
    }
}

/* Swift 3 
 * Provided it as a computed property instead of a function as a personal preference.
 */

import Foundation
import UIKit

public extension UIFont {
    
    public func withTraits(_ traits: UIFontDescriptorSymbolicTraits...) -> UIFont {
        let descriptor = self.fontDescriptor
            .withSymbolicTraits(UIFontDescriptorSymbolicTraits(traits))
        return UIFont(descriptor: descriptor!, size: 0)
    }
        
    public var italic : UIFont {
        return withTraits(.traitItalic)
    }
        
    public var bold : UIFont {
        return withTraits(.traitBold)
    }
}

Can we have some more italic font guide for other Font Weights like ultraLight, medium, etc?

Review this: (working fine on my end)

extension UIFont {
      
    class func italicSystemFont(ofSize size: CGFloat, weight: UIFont.Weight = .regular)-> UIFont {
        let font = UIFont.systemFont(ofSize: size, weight: weight)
        switch weight {
        case .ultraLight, .light, .thin, .regular:
            return font.withTraits(.traitItalic, ofSize: size)
        case .medium, .semibold, .bold, .heavy, .black:
            return font.withTraits(.traitBold, .traitItalic, ofSize: size)
        default:
            return UIFont.italicSystemFont(ofSize: size)
        }
    }
    
    func withTraits(_ traits: UIFontDescriptor.SymbolicTraits..., ofSize size: CGFloat) -> UIFont {
        let descriptor = self.fontDescriptor
            .withSymbolicTraits(UIFontDescriptor.SymbolicTraits(traits))
        return UIFont(descriptor: descriptor!, size: size)
    }
      
}

Usage:

myLabel.font = UIFont.italicSystemFont(ofSize: 34, weight: .ultraLight)
myLabel2.font = UIFont.italicSystemFont(ofSize: 34, weight: .black)

Review this: (working fine on my end)

extension UIFont {
      
    class func italicSystemFont(ofSize size: CGFloat, weight: UIFont.Weight = .regular)-> UIFont {
        let font = UIFont.systemFont(ofSize: size, weight: weight)
        switch weight {
        case .ultraLight, .light, .thin, .regular:
            return font.withTraits(.traitItalic, ofSize: size)
        case .medium, .semibold, .bold, .heavy, .black:
            return font.withTraits(.traitBold, .traitItalic, ofSize: size)
        default:
            return UIFont.italicSystemFont(ofSize: size)
        }
    }
    
    func withTraits(_ traits: UIFontDescriptor.SymbolicTraits..., ofSize size: CGFloat) -> UIFont {
        let descriptor = self.fontDescriptor
            .withSymbolicTraits(UIFontDescriptor.SymbolicTraits(traits))
        return UIFont(descriptor: descriptor!, size: size)
    }
      
}

Usage:

myLabel.font = UIFont.italicSystemFont(ofSize: 34, weight: .ultraLight)
myLabel2.font = UIFont.italicSystemFont(ofSize: 34, weight: .black)

You saved my life man ! Thanks