Kotlin Basic Learning - series 5

通过Kotlin的操作符重载可以让你写kotlin变得更快，像Path，Range或者SpannableStrings允许操作符“addition”或者“substraction”等， 你可以实现自己的操作符，比如：

/** Adds a span to the entire text. **/
inline operator fun Spannable.plusAssign(span: Any) = 
 setSpan(span, 0, length, SPAN_INCLUSIVE_EXCLUSIVE)

//Use it like this
val spannable = "Eureka!!!!".toSpannable()
spannable += StyleSpan(BOLD) // Make the text bold with +=
spannable += UnderlineSpan() // Make the text underline with +=

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

如果一个class有Utility的方法，请将他们添加到文件的最顶端， 在java中它们被编译成static的方法

// Define a top-level function that creates a DataBinding Adapter for a RecyclerView
@BindingAdapter("userItems")
fun userItems(recyclerView: RecyclerView, list: List<User>?) {
    // update the RecyclerView with the new list
}

Basic Syntax - Kotlin Programming Languagekotlinlang.org

Android KTX添加了在ViewGroup和SparseArray中添加了iterators（区别Sequences见Series 4）。定义iterator的extensions，需要使用‘operator’关键字。Foreach loops就可以使用extensions

// Example from Android KTX
for (view in ViewGroup) {}
for (key in sparseArray.keyIterator()) {}

// Your project
// add an iterator to a Waterfall
operator fun Waterfall.iterator() = // ... extend waterfall to have iterator
for (items in waterfall) {} // now waterfall can iterate!

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

Android使用KTX的Content Values可以让Kotlin写起来更加的简洁，也可以传入Pair<StringKey, Value>参数。

val contentValues = contentValuesOf(
    "KEY_INT" to 1, 
    "KEY_LONG" to 2L,
    "KEY_BOOLEAN" to true,
    "KEY_NULL" to null
)

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

Kotlin还支持Domain Specific Language

html {
    head {
        title {+"This is Kotlin!"}
    }
    body {
        h1 {+"A DSL defined in Kotlin!"}
        p {+"It's rather"
         b {+"bold."}
           + "don't you think?"
        }
    }
}

Type-Safe Builders - Kotlin Programming Languagekotlinlang.org

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