1. Android的KTX实现了Kotlin中的reified type parameters，这样一来，就可以不用再传递class的参数给我们的函数，比如：

   // the old way
   var alarmManager = context.getSystemService(AlarmManager::class.java)
   
   // the reified way
   var alarmManager: AlarmManager = context.systemService()
   // or
   var alarmManager = context.systemService<AlarmManager>()
   
   // the magic from Android KTX... with "real" type T
   inline fun <reified T> Context.systemService() = getSystemService(T::class.java)
   
   //previously 
   fun <T> TreeNode.findParentOfType(clazz: Class<T>): T? {
       var p = parent
       while (p != null && !clazz.isInstance(p)) {
           p = p.parent
       }
       @Suppress("UNCHECKED_CAST")
       return p as T?
   }
   // call
   treeNode.findParentOfType(MyTreeNode::class.java)
   
   // actually we want pass a type to this funciton, like:
   treeNode.findParentOfType<MyTreeNode>()
   // enable this, try use reified modifier
   inline fun <reified T> TreeNode.findParentOfType(): T? {
       var p = parent
       while (p != null && p !is T) {
           p = p.parent
       }
       return p as T?
   }
   

   Inline Functions and Reified Type Parameters - Kotlin Programming Languagekotlinlang.org

2. 通过关键字“by”可以将你的工作委托给另外一个class，在前面系列的lazy中其实已经提到过了。

   class MyAnimatingView: View(/*...*/) {
       // delegated property. Uses the getter and setter defined in InvalidateDelegeate
       var foregroundX by InvalidateDelegate(0f)
   }
   
   // A View Delegate which invalidates View.postInvalidateOnAnimation when set.
   class InvalidateDelegate<T: Any>(var value: T) {
       operator fun getValue(thisRef: View, property: KProperty<*>) = value
       operator fun setValue(thisRef: View, property: KProperty<*>, value: T) {
           this.value = value
           this.Ref.postInvalidateOnAnimation()
       }
   }
   

   Delegated Properties - Kotlin Programming Languagekotlinlang.org

3. No more Util classes。可以通过“extension functions”实现。在你想要添加方法的前面放上class的名字即可。比如：

   // Exten String with toUri
   inline fun String.toUri(): Uri = Uri.parse(this)
   
   // And call it on any String!
   val myUri = "www.developer.android.com".toUri()
   

   android/android-ktxandroid-ktx - A set of Kotlin extensions for Android app development.github.com

4. 在Android里面如果我们要实现一个从Drawable转换到Bitmap，就会需要一系列的步骤。但Android KTX提供了一些方法，让你的代码更加的简洁。（可以查看graphics package）

   // get a drawable from resources
   val myDrawable = ContextCompat.getDrawable(context, R.drawable.icon)
   
   //convert the drawable to a bitmap
   val bitmap = myDrawable.toBitmap()
   

   android/android-ktxandroid-ktx - A set of Kotlin extensions for Android app development.github.com

5. Sequence和Iterator很像，但Sequence其实perform lazily当你需要的时候，比如调的它的时候，但是Iterator更像是马上执行返回另外一个Iterable，如：

   // Sequence<T>.map { ... }
   val seq = sequenceOf(1, 2)
   val seqMapped: Sequence<Int> = seq.map { print("$it "); it * it } // intermediate
   print("before sum ")
   val sum = seqMapped.sum() // terminal
   
   // prints:
   // before sum 1 2
   

   // Iterable<T>.map { ... }
   val lst = listOf(1, 2)
   val lstMapped: List<Int> = lst.map { print("$it "); it * it }
   print("before sum ")
   val sum = lstMapped.sum()
   
   // prints:
   // 1 2 before sum
   

   val sequence = List(50) {it * 5}.asSequence
   sequence.map {it * 2}         // lazy(iterate 1 element at a time)
        .filter {it % 3 == 0} // lazy(iterate 1 element at a time)
        .map {it + 1}         // lazy(iterate 1 element at a time)
        .toList {}            // eager (iterate all elemnts)
   

kotlin.sequences - Kotlin Programming Languagekotlinlang.org