CompleteRunSnippet.swift

var animations = [CABasicAnimation]()
let rootAttributesKey = keyPath(\LKLabelLayer.currentTextDidChangeAnimation?
                                                            .interpolatedAttributeStates)
type(of: self).attributedStringKeys.forEach { (attributeRawValue) in

    var shorterTextValue : AnyObject? = nil
    let attributedStringKey = NSAttributedString.Key(rawValue: attributeRawValue)
    let swapped = self.toAttributedText?.length ?? 0 > self.fromAttributedText?.length ?? 0
    let longerText = swapped ? self.toAttributedText : self.fromAttributedText
    let shorterText = swapped ? self.fromAttributedText : self.toAttributedText
    
    longerText?.enumerateAttribute(attributedStringKey, 
                               in: NSMakeRange(0, longerText?.length ?? 0), 
                          options: [], 
                            using: { (longerTextValue, longerTextRange, longerTextStop) in
                            
        let isLastLongerTextRange = NSMaxRange(longerTextRange) == longerText?.length
        if shorterText != nil && longerTextRange.location < shorterText!.length {
        
            let toEnumerationRange = isLastLongerTextRange ? 
                            NSMakeRange(longerTextRange.location, 
                                        shorterText!.length - longerTextRange.location) : 
                            longerTextRange
                            
            shorterText!.enumerateAttribute(attributedStringKey, 
                                        in: toEnumerationRange, 
                                   options: [], 
                                     using: { (value, shorterTextRange, shorterTextStop) in
                shorterTextValue = value as AnyObject
                
                if (longerTextValue != nil || shorterTextValue != nil) && 
                  !(longerTextValue as AnyObject).isEqual(shorterTextValue) {
                  
                    let fromValue = swapped ? shorterTextValue : longerTextValue
                    let toValue = swapped ? longerTextValue : shorterTextValue
                    animations.append(contentsOf: 
                                      type(of: self).animationsForAttributeDiff(
                                                       forRootKey:rootAttributesKey, 
                                             attributedStringKey: attributedStringKey, 
                                                       fromValue: fromValue, 
                                                         toValue: toValue, 
                                                              in: shorterTextRange, 
                                                 attributeStates: self.interpolatedAttributeStates, 
                                                        duration: duration))
                }
            })
            if (shorterText == nil || NSMaxRange(longerTextRange) > shorterText!.length) && 
               (longerTextValue != nil || shorterTextValue != nil) && 
               !(longerTextValue as AnyObject).isEqual(shorterTextValue) {
               
                let fromValue = swapped ? shorterTextValue : longerTextValue
                let toValue = swapped ? longerTextValue : shorterTextValue
                animations.append(contentsOf: 
                                  type(of: self).animationsForAttributeDiff(
                                                       forRootKey: rootAttributesKey, 
                                              attributedStringKey: attributedStringKey, 
                                                        fromValue: fromValue, 
                                                          toValue: toValue, 
                                                               in: longerTextRange, 
                                                  attributeStates: self.interpolatedAttributeStates, 
                                                         duration: duration))
            }
        }
    })
}
if animations.count > 0 {
    self.animations = animations
    self.duration = duration
    self.timingFunction = CAMediaTimingFunction(name: .easeInEaseOut )
    textLayer.add(self, forKey: keyPath(\LKLabelLayer.attributedText))
}