Kotlin-36.类型安全的构建器/生成器(Type-Safe|Kotlin-36.类型安全的构建器/生成器(Type-Safe Builders)

官方文档: http://kotlinlang.org/docs/reference/type-safe-builders.html
1.类型安全的构建器(Type-Safe Builders)

构建器(builder)的概念在Groovy社区中非常热门, 构建器允许以半声明(semi-declarative)方式定义数据 构建器很适合用来生成XML, UI布局, 描述3D场景...多数情况下,Kotlin允许检查类型(type-check)构建器,比Groovy自身的动态类型实现更具吸引力; 其它情况下,Kotlin支持动态类型构建器

2.Html构建器(生成器)示例 【Kotlin-36.类型安全的构建器/生成器(Type-Safe|Kotlin-36.类型安全的构建器/生成器(Type-Safe Builders)】本例使用kotlin构建/生成一个HTML树(文档),
代码中大量使用了前几章节kotlin的扩展函数和带接收者的lambda表达式,
并没有新kotlin语法知识!
fun main(args: Array) { val result = html { head { title { +"XML encoding with Kotlin" } } body { h1 { +"XML encoding with Kotlin" } p { +"this format can be used as an alternative markup to XML" } a(href = "http://lioil.com") { +"Kotlin博客" } p { +"This is some" b { +"mixed" } +"text. For more see the" a(href = "http://lioil.com") { +"Kotlin博客" } +"project" } p { +"some text" } p { +"Command line arguments were:" ul {for (arg in args) li { +arg }} //命令行参数args } } } println(result) //输出一个Html树形文档,输出结果在下文 }/* init参数本身就是一个函数,该函数类型是HTML.() -> Unit,该函数带接收者是HTML类 html { //head和body是HTML的成员函数, this可以省略(this就是HTML类对象) this.head { } this.body { } } */ fun html(init: HTML.() -> Unit): HTML { val html = HTML() html.init() return html }/* String.unaryPlus()重载操作符+, 作用就是把一个字符串包装到TextElement实例对象, 并添加到children标签html集合,例如: title { +"XML encoding with Kotlin" } */ abstract class TagWithText(name: String) : Tag(name) { operator fun String.unaryPlus() { children.add(TextElement(this)) } }// 以下几个类,就是生成HTML标签元素 class HTML() : TagWithText("html") { fun head(init: Head.() -> Unit) = initTag(Head(), init) fun body(init: Body.() -> Unit) = initTag(Body(), init) } class Head() : TagWithText("head") { fun title(init: Title.() -> Unit) = initTag(Title(), init) } class Title() : TagWithText("title") class Body() : BodyTag("body") class UL() : BodyTag("ul") { fun li(init: LI.() -> Unit) = initTag(LI(), init) } class B() : BodyTag("b") class LI() : BodyTag("li") class P() : BodyTag("p") class H1() : BodyTag("h1") class A() : BodyTag("a") { public var href: String get() = attributes["href"]!! set(value) { attributes["href"] = value } }interface Element { fun render(builder: StringBuilder, indent: String) }class TextElement(val text: String) : Element { override fun render(builder: StringBuilder, indent: String) { builder.append("$indent$text\n") } }@DslMarker annotation class HtmlTagMarker/* 自Kotlin 1.1起,引入了一种特殊机制,控制接收者作用域(Scope control: @DslMarker) 不必用@HtmlTagMarker标注HTML或Head类,因为它们的超类/父类Tag已标注过! 添加注解HtmlTagMarker之后,Kotlin编译器就知道哪些隐式接收者是同一个DSL, 并且只允许调用最近层的接收者的成员 html { head { head { } // 错误: head是外部接收者的成员 } // …… }注意:仍然可以调用外部接收者的成员,但必须明确指定该接收者: html { head { this@html.head { } // 可行 } // …… } */ @HtmlTagMarker abstract class Tag(val name: String) : Element { val children = arrayListOf() val attributes = hashMapOf()protected fun initTag(tag: T, init: T.() -> Unit): T { tag.init() children.add(tag) return tag }override fun render(builder: StringBuilder, indent: String) { builder.append("$indent<$name${renderAttributes()}>\n") for (c in children) { c.render(builder, indent + "") } builder.append("$indent\n") }private fun renderAttributes(): String? { val builder = StringBuilder() for (a in attributes.keys) { builder.append(" $a=\"${attributes[a]}\"") } return builder.toString() }override fun toString(): String { val builder = StringBuilder() render(builder, "") return builder.toString() } }abstract class BodyTag(name: String) : TagWithText(name) { fun b(init: B.() -> Unit) = initTag(B(), init) fun p(init: P.() -> Unit) = initTag(P(), init) fun h1(init: H1.() -> Unit) = initTag(H1(), init) fun ul(init: UL.() -> Unit) = initTag(UL(), init) fun a(href: String, init: A.() -> Unit) { val a = initTag(A(), init) a.href = https://www.it610.com/article/href } }

2.Html构建器(生成器)的输出结果
XML encoding with Kotlin - 锐客网 XML encoding with Kotlinthis format can be used as an alternative markup to XML
Kotlin博客This is some mixedtext. For more see the Kotlin博客 project
some text
Command line arguments were:
  • lioil
  • win


:http://www.jianshu.com/p/70cbaf846a4f
CSDN博客: http://blog.csdn.net/qq_32115439/article/details/74898099
GitHub博客:http://lioil.win/2017/07/09/Kotlin-safe-builder.html
Coding博客:http://c.lioil.win/2017/07/09/Kotlin-safe-builder.html

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