Kotlin系列之Lambda编译成字节码过程完全解析

爱被打了一巴掌 2022-05-26 09:51 364阅读 0赞

**简述:** 今天带来的是Kotlin浅谈系列第七弹，上篇博客我们聊到关于Kotlin中的lambda表达式的一些语法规则和基本使用。然而我们并没有聊到Kotlin的lambda表达式的本质是什么?我们都知道使用Kotlin来开发Android,最终都会编译成字节码文件.class，然后字节码文件run到JVM上，最后整个应用跑起来。

*  1、为什么需要去对lambda表达式字节码分析？(why)
 *  2、lambda表达式实质原理是什么？(what)
 *  3、lambda表达式字节码查看工具的使用
 *  4、kotlin中@Metadata注解详解
 *  5、如何去分析lambda表达式字节码(how)
 *  6、使用lambda表达式时的性能优化
 *  7、使用lambda表达式需要注意哪些问题

### 一、为什么需要去对lambda表达式字节码分析? ###

Kotlin中的lambda表达式给使用者的感知它就是一个很简洁的语法糖，但是在简洁语法糖背后内容你有所了解吗？学会分析lambda表达式编译成字节码的整个过程，会对高效率地去使用lambda表达式会有很大帮助，否则就会很容出现lambda表达式滥用的情况，这种情况非常影响程序性能。所以需要从真正本质上去完全理解lambda是什么？以及它是如何编译成对应class。

### 二、lambda表达式实质原理 ###

Kotlin中的lambda表达式实际上最后会编译为一个class类，这个类会去继承Kotlin中Lambda的抽象类(在kotlin.jvm.internal包中)并且实现一个FunctionN(在kotlin.jvm.functions包中)的接口(这个N是根据lambda表达式传入参数的个数决定的,目前接口N的取值为 0 <= N <= 22,也就是lambda表达式中函数传入的参数最多也只能是22个)，这个Lambda抽象类是实现了FunctionBase接口，该接口中有两个方法一个是getArity()获取lambda参数的元数，toString()实际上就是打印出Lambda表达式类型字符串，获取Lambda表达式类型字符串是通过Java中Reflection类反射来实现的。FunctionBase接口继承了Function,Serializable接口。来看一个简单的lambda例子

package com.mikyou.kotlin.lambda.simple
    
    typealias Sum = (Int, Int, Int) -> Int
    
    fun main(args: Array<String>) {
        
        val sum: Sum = {
         a, b, c ->//定义一个很简单的三个数求和的lambda表达式
            a + b + c
        }
    
        println(sum.invoke(1, 2, 3))
    }

lambda调用处反编译后的代码

package com.mikyou.kotlin.lambda.simple;
    
    import kotlin.Metadata;
    import kotlin.jvm.functions.Function3;
    import kotlin.jvm.internal.Intrinsics;
    import org.jetbrains.annotations.NotNull;
    
    @Metadata(
       mv = {
        1, 1, 10},
       bv = {
        1, 0, 2},
       k = 2,
       d1 = {
        "\u0000\u001e\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0002\b\u0002\n\u0002\u0018\u0002\n\u0002\u0010\b\n\u0000\u001a\u0019\u0010\u0000\u001a\u00020\u00012\f\u0010\u0002\u001a\b\u0012\u0004\u0012\u00020\u00040\u0003¢\u0006\u0002\u0010\u0005*:\u0010\u0006\"\u001a\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u00072\u001a\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u0007¨\u0006\t"},
       d2 = {
        "main", "", "args", "", "", "([Ljava/lang/String;)V", "Sum", "Lkotlin/Function3;", "", "production sources for module Lambda_main"}
    )
    public final class SumLambdaKt {
        
       public static final void main(@NotNull String[] args) {
        
          Intrinsics.checkParameterIsNotNull(args, "args");
          Function3 sum = (Function3)null.INSTANCE;//实例化的是FunctionN接口中Function3，因为有三个参数
          int var2 = ((Number)sum.invoke(1, 2, 3)).intValue();
          System.out.println(var2);
       }
    }

lambda反编译后的代码

package com.mikyou.kotlin.lambda.simple;
    
    import kotlin.jvm.internal.Lambda;
    
    @kotlin.Metadata(mv = {
        1, 1, 10}, bv = {
        1, 0, 2}, k = 3, d1 = {
        "\000\n\n\000\n\002\020\b\n\002\b\004\020\000\032\0020\0012\006\020\002\032\0020\0012\006\020\003\032\0020\0012\006\020\004\032\0020\001H\n¢\006\002\b\005"}, d2 = {
        "<anonymous>", "", "a", "b", "c", "invoke"})
    final class SumLambdaKt$main$sum$1 extends Lambda implements kotlin.jvm.functions.Function3<Integer, Integer, Integer, Integer> {
        
        public final int invoke(int a, int b, int c) {
        
            return a + b + c;
        }
    
        public static final SumLambdaKt$main$sum$1 INSTANCE =new SumLambdaKt$main$sum$1();
    
        SumLambdaKt$main$sum$1() {
        
            super(3);//这个super传入3,也就是前面getArity获得参数的元数和函数参数个数一致
        }
    }

### 三、lambda表达式字节码查看工具的使用 ###

既然是分析字节码class文件，所以必须得有个字节码查看工具，你可以使用JD-GUI或者其他的，我这里使用的是BytecodeViewer,它核心实现也是基于JD-GUI的。任意选择一款字节码查看工具都可以，这里是[BytecodeViewer][]的下载地址有需要可以去下载，它的使用也是非常简单的。

*  1、下载完毕后，打开主界面(界面有点粗糙，这个可以忽略)

![163077d3d55a094e_w_1188_h_755_f_jpeg_s_133209][]

*  2、然后，只需要把相应的.class文件拖入文件选择区，就可以查看相应反编译的Java代码和字节码

![163077cf2e40f577_w_1176_h_750_f_jpeg_s_547145][]

### 四、kotlin中@Metadata注解详解 ###

从刚刚反编译的代码，有个@Metadata注解很是引入注意，它到底是个啥？每个Kotlin代码反编译成Java代码都会有这个@Metadata注解。为了更好地去理解这个字节码生成的过程，我觉得有必要去了解一下，它们每一个的含义。

#### 1、@Metadata注解介绍及生成流程 ####

kotlin中的@Metadata注解是一个很特殊的注解，它记录了Kotlin代码中的一些信息，比如 class 的可见性，function 的返回值，参数类型，property 的 lateinit，nullable 的属性，typealias类型别名声明等。我们都知道Kotlin代码最终都要转化成Java的字节码的，然后运行JVM上。但是Kotlin代码和Java代码差别还是很大的，一些Kotlin特殊语言特性是独有的(比如lateinit, nullable, typealias)，所以需要记录一些信息来标识Kotlin中的一些特殊语法信息。最终这些信息都是有kotlinc编译器生成，并以注解的形式存在于字节码文件中。

![16307956d8888bce_w_1241_h_201_f_png_s_25476][]

#### 2、@Metadata注解的状态 ####

通过上面转化图可得知，@Metadata注解会一直保存在class字节码中，也就是这个注解是一个运行时的注解，在RunTime的时候会一直保留，那么可以通过反射可以拿到，并且这个@Metadata注解是Kotlin独有的，也就是Java是不会生成这样的注解存在于.class文件中，也就是从另一方面可以通过反射可以得知这个类是不是Kotlin的class.

#### 3、@Metadata注解源码中每个参数的含义 ####

@Metadata注解源码

package kotlin
    
    /**
     * This annotation is present on any class file produced by the Kotlin compiler and is read by the compiler and reflection.
     * Parameters have very short names on purpose: these names appear in the generated class files, and we'd like to reduce their size.
     */
    @Retention(AnnotationRetention.RUNTIME)
    @Target(AnnotationTarget.CLASS)
    internal annotation class Metadata(
            /**
             * A kind of the metadata this annotation encodes. Kotlin compiler recognizes the following kinds (see KotlinClassHeader.Kind):
             *
             * 1 Class
             * 2 File
             * 3 Synthetic class
             * 4 Multi-file class facade
             * 5 Multi-file class part
             *
             * The class file with a kind not listed here is treated as a non-Kotlin file.
             */
            val k: Int = 1,
            /**
             * The version of the metadata provided in the arguments of this annotation.
             */
            val mv: IntArray = intArrayOf(),
            /**
             * The version of the bytecode interface (naming conventions, signatures) of the class file annotated with this annotation.
             */
            val bv: IntArray = intArrayOf(),
            /**
             * Metadata in a custom format. The format may be different (or even absent) for different kinds.
             */
            val d1: Array<String> = arrayOf(),
            /**
             * An addition to [d1]: array of strings which occur in metadata, written in plain text so that strings already present
             * in the constant pool are reused. These strings may be then indexed in the metadata by an integer index in this array.
             */
            val d2: Array<String> = arrayOf(),
            /**
             * An extra string. For a multi-file part class, internal name of the facade class.
             */
            val xs: String = "",
            /**
             * Fully qualified name of the package this class is located in, from Kotlin's point of view, or empty string if this name
             * does not differ from the JVM's package FQ name. These names can be different in case the [JvmPackageName] annotation is used.
             * Note that this information is also stored in the corresponding module's `.kotlin_module` file.
             */
            val pn: String = "",
            /**
             * An extra int. Bits of this number represent the following flags:
             *
             * 0 - this is a multi-file class facade or part, compiled with `-Xmultifile-parts-inherit`.
             * 1 - this class file is compiled by a pre-release version of Kotlin and is not visible to release versions.
             * 2 - this class file is a compiled Kotlin script source file (.kts).
             */
            @SinceKotlin("1.1")
            val xi: Int = 0
    )

注意: @Metadata注解中的k,mv,d1,d2…都是简写，为什么要这样做呢?说白了就是为了class文件的大小，尽可能做到精简。

<table> 
 <thead> 
  <tr> 
   <th align="left">参数简写名称</th> 
   <th align="left">参数全称</th> 
   <th align="left">参数类型</th> 
   <th align="left">参数取值</th> 
   <th align="left">参数含义</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">k</td> 
   <td align="left">kind</td> 
   <td align="left">Int</td> 
   <td align="left">1: class,表示这个kotlin文件是一个类或者接口<br>2: file,表示这个kotin文件是一个.kt结尾的文件<br>3: Synthetic class,表示这个kotlin文件是一个合成类<br>4(Multi-file class facade)<br>5(Multi-file class part)</td> 
   <td align="left">表示当前metadata注解编码种类</td> 
  </tr> 
  <tr> 
   <td align="left">mv</td> 
   <td align="left">metadata version</td> 
   <td align="left">IntArray</td> 
   <td align="left">-</td> 
   <td align="left">metadata版本号</td> 
  </tr> 
  <tr> 
   <td align="left">bv</td> 
   <td align="left">bytecode version</td> 
   <td align="left">IntArray</td> 
   <td align="left">-</td> 
   <td align="left">字节码版本号</td> 
  </tr> 
  <tr> 
   <td align="left">d1</td> 
   <td align="left">data1</td> 
   <td align="left">Array&lt;String&gt;</td> 
   <td align="left">-</td> 
   <td align="left">主要记录Kotlin语法信息</td> 
  </tr> 
  <tr> 
   <td align="left">d2</td> 
   <td align="left">data2</td> 
   <td align="left">Array&lt;String&gt;</td> 
   <td align="left">-</td> 
   <td align="left">主要记录Kotlin语法信息</td> 
  </tr> 
  <tr> 
   <td align="left">xs</td> 
   <td align="left">extra String</td> 
   <td align="left">String</td> 
   <td align="left">-</td> 
   <td align="left">主要是为多文件的类(Multi-file class)预留的名称</td> 
  </tr> 
  <tr> 
   <td align="left">xi</td> 
   <td align="left">extra Int</td> 
   <td align="left">Int</td> 
   <td align="left">0 (表示一个多文件的类Multi-file class facade或者多文件类的部分Multi-file class part编译成-Xmultifile-parts-inherit)<br>1 (表示此类文件由Kotlin的预发行版本编译，并且对于发行版本不可见)<br>2 (表示这个类文件是一个编译的Kotlin脚本源文件)</td> 
   <td align="left">-</td> 
  </tr> 
  <tr> 
   <td align="left">pn</td> 
   <td align="left">fully qualified name of package</td> 
   <td align="left">String</td> 
   <td align="left">-</td> 
   <td align="left">主要记录kotlin类完整的包名</td> 
  </tr> 
 </tbody> 
</table>

#### 4、实例分析@Metadata注解 ####

kotlin源码，定义的是一个.kt结尾文件

package com.mikyou.kotlin.lambda.simple
    
    typealias Sum = (Int, Int, Int) -> Int//typealias关键字声明lambda表达式类型别名
    
    fun main(args: Array<String>) {
        
        val sum: Sum = {
         a, b, c ->//定义一个很简单的三个数求和的lambda表达式
            a + b + c
        }
    
        println(sum.invoke(1, 2, 3))
    }

反编译后Java代码

package com.mikyou.kotlin.lambda.simple;
    
    import kotlin.Metadata;
    import kotlin.jvm.functions.Function3;
    import kotlin.jvm.internal.Intrinsics;
    import org.jetbrains.annotations.NotNull;
    
    @Metadata(
       mv = {
        1, 1, 10},
       bv = {
        1, 0, 2},
       k = 2,
       d1 = {
        "\u0000\u001e\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0002\b\u0002\n\u0002\u0018\u0002\n\u0002\u0010\b\n\u0000\u001a\u0019\u0010\u0000\u001a\u00020\u00012\f\u0010\u0002\u001a\b\u0012\u0004\u0012\u00020\u00040\u0003¢\u0006\u0002\u0010\u0005*:\u0010\u0006\"\u001a\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u00072\u001a\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u0007¨\u0006\t"},
       d2 = {
        "main", "", "args", "", "", "([Ljava/lang/String;)V", "Sum", "Lkotlin/Function3;", "", "production sources for module Lambda_main"}
    )
    public final class SumLambdaKt {
        
       public static final void main(@NotNull String[] args) {
        
          Intrinsics.checkParameterIsNotNull(args, "args");
          Function3 sum = (Function3)SumLambdaKt$main$sum$1.INSTANCE;
          int var2 = ((Number)sum.invoke(1, 2, 3)).intValue();
          System.out.println(var2);
       }
    }

*  **k = 2 表示的是这是一个.kt结尾的kotlin文件**
 *  **mv = \{1,1,10\} 表示metadata版本号是1.1.10**
 *  **bv = \{1,0,2\} 表示bytecode版本号是1.0.2**
 *  **d1 = \{…\} 里面的信息是经过了 protobuf 编码的二进制流 具体可见[详细描述][Link 1]**
 *  **d2 = \{“main”, “”, “args”, “”, “”, “(\[Ljava/lang/String;)V”, “Sum”, “Lkotlin/Function3;”, “”, “production sources for module Lambda\_main”\}表示记录有main函数，已经main函数参数名称args，Sum就是通过typealias取lambda表达式类型别名，Lkotlin/Function3声明的是Lambda表达式中生成的这个类是实现了FunctionN中Function3接口，因为它对应只有三个参数**

kotlin中定义一个类源码

package com.mikyou.kotlin.lambda
    
    /**
     * Created by mikyou on 2018/3/27.
     */
    data class Person(val name: String, val age: Int)

反编译后Java代码

package com.mikyou.kotlin.lambda;
    
    import kotlin.Metadata;
    import kotlin.jvm.internal.Intrinsics;
    import org.jetbrains.annotations.NotNull;
    
    @Metadata(
       mv = {
        1, 1, 10},
       bv = {
        1, 0, 2},
       k = 1,//kind就是变成了1，表示这是一个kotlin的class类
       d1 = {
        "\u0000 \n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0000\n\u0002\u0010\u000e\n\u0000\n\u0002\u0010\b\n\u0002\b\t\n\u0002\u0010\u000b\n\u0002\b\u0004\b\u0086\b\u0018\u00002\u00020\u0001B\u0015\u0012\u0006\u0010\u0002\u001a\u00020\u0003\u0012\u0006\u0010\u0004\u001a\u00020\u0005¢\u0006\u0002\u0010\u0006J\t\u0010\u000b\u001a\u00020\u0003HÆ\u0003J\t\u0010\f\u001a\u00020\u0005HÆ\u0003J\u001d\u0010\r\u001a\u00020\u00002\b\b\u0002\u0010\u0002\u001a\u00020\u00032\b\b\u0002\u0010\u0004\u001a\u00020\u0005HÆ\u0001J\u0013\u0010\u000e\u001a\u00020\u000f2\b\u0010\u0010\u001a\u0004\u0018\u00010\u0001HÖ\u0003J\t\u0010\u0011\u001a\u00020\u0005HÖ\u0001J\t\u0010\u0012\u001a\u00020\u0003HÖ\u0001R\u0011\u0010\u0004\u001a\u00020\u0005¢\u0006\b\n\u0000\u001a\u0004\b\u0007\u0010\bR\u0011\u0010\u0002\u001a\u00020\u0003¢\u0006\b\n\u0000\u001a\u0004\b\t\u0010\n¨\u0006\u0013"},
       d2 = {
        "Lcom/mikyou/kotlin/lambda/Person;", "", "name", "", "age", "", "(Ljava/lang/String;I)V", "getAge", "()I", "getName", "()Ljava/lang/String;", "component1", "component2", "copy", "equals", "", "other", "hashCode", "toString", "production sources for module Lambda_main"}
    )
    public final class Person {
        
       @NotNull
       private final String name;
       private final int age;
    
       @NotNull
       public final String getName() {
        
          return this.name;
       }
    
       public final int getAge() {
        
          return this.age;
       }
    
       public Person(@NotNull String name, int age) {
        
          Intrinsics.checkParameterIsNotNull(name, "name");
          super();
          this.name = name;
          this.age = age;
       }
    
       @NotNull
       public final String component1() {
        
          return this.name;
       }
    
       public final int component2() {
        
          return this.age;
       }
    
       @NotNull
       public final Person copy(@NotNull String name, int age) {
        
          Intrinsics.checkParameterIsNotNull(name, "name");
          return new Person(name, age);
       }
    
       // $FF: synthetic method
       @NotNull
       public static Person copy$default(Person var0, String var1, int var2, int var3, Object var4) {
        
          if ((var3 & 1) != 0) {
        
             var1 = var0.name;
          }
    
          if ((var3 & 2) != 0) {
        
             var2 = var0.age;
          }
    
          return var0.copy(var1, var2);
       }
    
       public String toString() {
        
          return "Person(name=" + this.name + ", age=" + this.age + ")";
       }
    
       public int hashCode() {
        
          return (this.name != null ? this.name.hashCode() : 0) * 31 + this.age;
       }
    
       public boolean equals(Object var1) {
        
          if (this != var1) {
        
             if (var1 instanceof Person) {
        
                Person var2 = (Person)var1;
                if (Intrinsics.areEqual(this.name, var2.name) && this.age == var2.age) {
        
                   return true;
                }
             }
    
             return false;
          } else {
        
             return true;
          }
       }
    }

#### 5、@Metadata注解需要注意的问题 ####

我们知道了@Metadata注解是会一直保留至运行时，而且在配置混淆一定需要注意，@Metadata注解保存的信息是会被proguard给干掉的，所以不能让proguard干掉，否则一些重要的信息就会丢失，那么这个.class文件就是无效的，run在JVM上是会抛异常的。

### 五、如何去分析lambda表达式字节码 ###

*  1、从Kotlin源码出发定义了一个三个数求和lambda表达式最后通过invoke()方法传入三个参数完成lambda表达式的调用。

package com.mikyou.kotlin.lambda.simple
    
    typealias Sum = (Int, Int, Int) -> Int //给类型取个别名
    
    fun main(args: Array<String>) {
        
        val sum: Sum = {
         a, b, c ->//定义一个很简单的三个数求和的lambda表达式
            a + b + c
        }
    
        println(sum.invoke(1, 2, 3))//invoke方法实现lambda表达式的调用
    }

*  2、然后再重点介绍几个类和接口。

Lambda抽象类:

/*
     * Copyright 2010-2015 JetBrains s.r.o.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     * http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    
    package kotlin.jvm.internal
    
    public abstract class Lambda(private val arity: Int) : FunctionBase {
        
        override fun getArity() = arity//实现FunctionBase接口中的抽象方法getArity(),并通过构造器把元数传给它
    
        override fun toString() = Reflection.renderLambdaToString(this)//toString()方法重写
    }

FunctionBase接口,继承了Function<R>接口和Serializable序列化接口(这是一个Java接口):

/*
     * Copyright 2010-2016 JetBrains s.r.o.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     * http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    
    package kotlin.jvm.internal;
    
    import kotlin.Function;
    
    import java.io.Serializable;
    
    public interface FunctionBase extends Function, Serializable {
        
        int getArity();//抽象方法getArity
    }

FunctionN系列的接口( 0 <= N <= 22)也继承了Function<R>接口,也就是目前支持的lambda表达式类型接收参数的个数不能超过22个,是不是突然感觉kotlin居然还有这种操作。并且每个接口中都有一个invoke抽象方法，用于外部调用lambda表达式。

/*
     * Copyright 2010-2018 JetBrains s.r.o.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     * http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    
    // Auto-generated file. DO NOT EDIT!
    
    package kotlin.jvm.functions
    
    /** A function that takes 0 arguments. */
    public interface Function0<out R> : Function<R> {
        
        /** Invokes the function. */
        public operator fun invoke(): R
    }
    /** A function that takes 1 argument. */
    public interface Function1<in P1, out R> : Function<R> {
        
        /** Invokes the function with the specified argument. */
        public operator fun invoke(p1: P1): R
    }
    /** A function that takes 2 arguments. */
    public interface Function2<in P1, in P2, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2): R
    }
    /** A function that takes 3 arguments. */
    public interface Function3<in P1, in P2, in P3, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3): R
    }
    /** A function that takes 4 arguments. */
    public interface Function4<in P1, in P2, in P3, in P4, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4): R
    }
    /** A function that takes 5 arguments. */
    public interface Function5<in P1, in P2, in P3, in P4, in P5, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5): R
    }
    /** A function that takes 6 arguments. */
    public interface Function6<in P1, in P2, in P3, in P4, in P5, in P6, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6): R
    }
    /** A function that takes 7 arguments. */
    public interface Function7<in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7): R
    }
    /** A function that takes 8 arguments. */
    public interface Function8<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8): R
    }
    /** A function that takes 9 arguments. */
    public interface Function9<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9): R
    }
    /** A function that takes 10 arguments. */
    public interface Function10<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10): R
    }
    /** A function that takes 11 arguments. */
    public interface Function11<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11): R
    }
    /** A function that takes 12 arguments. */
    public interface Function12<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12): R
    }
    /** A function that takes 13 arguments. */
    public interface Function13<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13): R
    }
    /** A function that takes 14 arguments. */
    public interface Function14<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14): R
    }
    /** A function that takes 15 arguments. */
    public interface Function15<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15): R
    }
    /** A function that takes 16 arguments. */
    public interface Function16<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16): R
    }
    /** A function that takes 17 arguments. */
    public interface Function17<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17): R
    }
    /** A function that takes 18 arguments. */
    public interface Function18<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18): R
    }
    /** A function that takes 19 arguments. */
    public interface Function19<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19): R
    }
    /** A function that takes 20 arguments. */
    public interface Function20<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20): R
    }
    /** A function that takes 21 arguments. */
    public interface Function21<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21): R
    }
    /** A function that takes 22 arguments. */
    public interface Function22<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> : Function<R> {
        
        /** Invokes the function with the specified arguments. */
        public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21, p22: P22): R
    }

Function<R>接口，我们都知道在kotlin中是可以把函数当做值来看待的，那么这个函数值也是有类型的，也就是函数类型，这个Function就是lambda、匿名函数、普通命名函数的函数引用类型。

/*
     * Copyright 2010-2015 JetBrains s.r.o.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     * http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */
    
    package kotlin
    
    /**
     * Represents a value of a functional type, such as a lambda, an anonymous function or a function reference.
     *
     * @param R return type of the function.
     */
    public interface Function<out R>

lambda编译后生成的class，通过生成字节码中的类可以看出，  
生成唯一的类名是这个lambda表达式声明处于哪个顶层文件(它生成规则之前博客有提到),哪个方法中，以及最终lambda表达式的名字组成， SumLambdaKt$main$sum$1, SumLambdaKt顶层文件名，在main函数声明的，lambda表达式名为sum,由于Kotlin中的lambda只有三个参数,那么这个Lambda类的arity元数也就是3，可以看到生成的类中构造器super(3)。然后就去实现了对应FunctionN接口也就是N=3，实现了Function3接口，重写了invoke方法。

package com.mikyou.kotlin.lambda.simple;
    
    import kotlin.jvm.internal.Lambda;
    
    @kotlin.Metadata(mv = {
        1, 1, 10}, bv = {
        1, 0, 2}, k = 3, d1 = {
        "\000\n\n\000\n\002\020\b\n\002\b\004\020\000\032\0020\0012\006\020\002\032\0020\0012\006\020\003\032\0020\0012\006\020\004\032\0020\001H\n¢\006\002\b\005"}, d2 = {
        "<anonymous>", "", "a", "b", "c", "invoke"})
    final class SumLambdaKt$main$sum$1 extends Lambda implements kotlin.jvm.functions.Function3<Integer, Integer, Integer, Integer> {
        
        public final int invoke(int a, int b, int c) {
        
            return a + b + c;
        }
    
        public static final SumLambdaKt$main$sum$1 INSTANCE =new SumLambdaKt$main$sum$1();//静态SumLambdaKt$main$sum$1的实例INSTANCE供外部调用
    
        SumLambdaKt$main$sum$1() {
        
            super(3);//这个super传入3,也就是前面getArity获得参数的元数和函数参数个数一致
        }
    }

为了清晰表达类与类之间关系请看下面这张类图

![1630a4327a4f6daa_w_553_h_1021_f_png_s_94428][]

调用处反编译的Java代码

package com.mikyou.kotlin.lambda.simple;
    
    import kotlin.Metadata;
    import kotlin.jvm.functions.Function3;
    import kotlin.jvm.internal.Intrinsics;
    import org.jetbrains.annotations.NotNull;
    
    @Metadata(
       mv = {
        1, 1, 10},
       bv = {
        1, 0, 2},
       k = 2,
       d1 = {
        "\u0000\u001e\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0002\b\u0002\n\u0002\u0018\u0002\n\u0002\u0010\b\n\u0000\u001a\u0019\u0010\u0000\u001a\u00020\u00012\f\u0010\u0002\u001a\b\u0012\u0004\u0012\u00020\u00040\u0003¢\u0006\u0002\u0010\u0005*:\u0010\u0006\"\u001a\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u00072\u001a\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u0007¨\u0006\t"},
       d2 = {
        "main", "", "args", "", "", "([Ljava/lang/String;)V", "Sum", "Lkotlin/Function3;", "", "production sources for module Lambda_main"}
    )
    public final class SumLambdaKt {
        
       public static final void main(@NotNull String[] args) {
        
          Intrinsics.checkParameterIsNotNull(args, "args");
          Function3 sum = (Function3)SumLambdaKt$main$sum$1.INSTANCE;//调用静态SumLambdaKt$main$sum$1的实例INSTANCE，强转成Function3类型。
          int var2 = ((Number)sum.invoke(1, 2, 3)).intValue();//然后用这个sum对象实例去调用Function3中三个参数的invoke方法
          System.out.println(var2);
       }
    }

最后我们再梳理一下整个编译的流程:

首先，定义好的Kotlin Lambda表达式，通过Lambda表达式的类型，可以得到参数的个数以及参数的类型，也就是向Lambda抽象类的构造器传递arity元数，Lambda抽象类又把arity传递给FunctionBase,在编译时期会根据这个arity元数动态确定需要实现FunctionN接口，然后通过实现了相应的FunctionN接口中的invoke方法，最后lambda表达式函数体内代码逻辑将会在invoke方法体内。整个编译的流程完毕，也就在本地目录会生成一个.class字节码文件。从调用处反编译的代码就会直接调用.class字节码中已经生成的类中的INSTANCE静态实例对象，最后通过这个实例去调用invoke方法。

![1630c2bf7d169bec_w_610_h_732_f_png_s_55803][]

### 六、使用lambda表达式时的性能优化 ###

我们都知道lambda表达式可以作为一个参数传入到另一个函数中，这个也称为高阶函数。在使用高阶函数的时候我们需要注意尽量把我们的高阶函数声明成inline内联函数，因为通过上面的字节码分析的编译过程知道lambda最终会被编译成一个FunctionN类，然后调用的地方是使用这个FunctionN的实例去调用相应invoke方法。如果声明成内联函数的话，那么将不会去生成这个类并且在函数调用处是不需要实例化这个FunctionN的实例，而是在调用的时把调用的方法给替换上去，可以降低很大的性能开销。一起来看个例子

没有设置inline函数的case:

package com.mikyou.kotlin.lambda.high
    
    typealias SumAlias = (Int, Int) -> Int
    
    fun printSum(a: Int, b: Int, block: SumAlias) {
        //没有设置inline关键字
        println(block.invoke(a, b))
    }
    
    fun main(args: Array<String>) {
        
        printSum(4, 5) {
         a, b ->
            a + b
        }
    }

编译生成.clas文件目录，一个是调用处生成的字节码，另一处则是声明Lambda表达式字节码:

![1630c5d980701d03_w_1684_h_120_f_png_s_54193][]

函数调用处生成的字节码

package com.mikyou.kotlin.lambda.high;
    
    import kotlin.Metadata;
    import kotlin.jvm.functions.Function2;
    import kotlin.jvm.internal.Intrinsics;
    import org.jetbrains.annotations.NotNull;
    
    @Metadata(
       mv = {
        1, 1, 10},
       bv = {
        1, 0, 2},
       k = 2,
       d1 = {
        "\u0000(\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0002\b\u0003\n\u0002\u0010\b\n\u0002\b\u0002\n\u0002\u0018\u0002\n\u0002\u0018\u0002\n\u0002\b\u0002\u001a\u0019\u0010\u0000\u001a\u00020\u00012\f\u0010\u0002\u001a\b\u0012\u0004\u0012\u00020\u00040\u0003¢\u0006\u0002\u0010\u0005\u001a4\u0010\u0006\u001a\u00020\u00012\u0006\u0010\u0007\u001a\u00020\b2\u0006\u0010\t\u001a\u00020\b2\u001c\u0010\n\u001a\u0018\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u000bj\u0002`\f*.\u0010\r\"\u0014\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u000b2\u0014\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u000b¨\u0006\u000e"},
       d2 = {
        "main", "", "args", "", "", "([Ljava/lang/String;)V", "printSum", "a", "", "b", "block", "Lkotlin/Function2;", "Lcom/mikyou/kotlin/lambda/high/SumAlias;", "SumAlias", "production sources for module Lambda_main"}
    )
    public final class SumHighFuntionKt {
        
       public static final void printSum(int a, int b, @NotNull Function2 block) {
        
          Intrinsics.checkParameterIsNotNull(block, "block");
          int var3 = ((Number)block.invoke(a, b)).intValue();
          System.out.println(var3);
       }
    
       public static final void main(@NotNull String[] args) {
        
          Intrinsics.checkParameterIsNotNull(args, "args");
          printSum(4, 5, (Function2)null.INSTANCE);//传入了Function2类型INSTANCE实例到printSum函数中
       }
    }

lambda声明处反编译的代码

package com.mikyou.kotlin.lambda.high;
    
    import kotlin.jvm.internal.Lambda;
    
    @kotlin.Metadata(mv = {
        1, 1, 10}, bv = {
        1, 0, 2}, k = 3, d1 = {
        "\000\n\n\000\n\002\020\b\n\002\b\003\020\000\032\0020\0012\006\020\002\032\0020\0012\006\020\003\032\0020\001H\n¢\006\002\b\004"}, d2 = {
        "<anonymous>", "", "a", "b", "invoke"})
    final class SumHighFuntionKt$main$1 extends Lambda implements kotlin.jvm.functions.Function2<Integer, Integer, Integer> {
        
        public static final 1INSTANCE =new 1();
    
        public final int invoke(int a, int b) {
        
            return a + b;
        }
    
        SumHighFuntionKt$main$1() {
        
            super(2);
        }
    }

设置inline函数的case:

package com.mikyou.kotlin.lambda.high
    
    typealias SumAlias = (Int, Int) -> Int
    
    inline fun printSum(a: Int, b: Int, block: SumAlias) {
        //设置inline,printSum为内联函数
        println(block.invoke(a, b))
    }
    
    fun main(args: Array<String>) {
        
        printSum(4, 5) {
         a, b ->
            a + b
        }
    }

编译生成.clas文件目录，只有一个调用处生成的字节码:

![1630c69a7284a7e1_w_1600_h_78_f_png_s_33636][]

函数调用处生成的字节码

package com.mikyou.kotlin.lambda.high;
    
    import kotlin.Metadata;
    import kotlin.jvm.functions.Function2;
    import kotlin.jvm.internal.Intrinsics;
    import org.jetbrains.annotations.NotNull;
    
    @Metadata(
       mv = {
        1, 1, 10},
       bv = {
        1, 0, 2},
       k = 2,
       d1 = {
        "\u0000(\n\u0000\n\u0002\u0010\u0002\n\u0000\n\u0002\u0010\u0011\n\u0002\u0010\u000e\n\u0002\b\u0003\n\u0002\u0010\b\n\u0002\b\u0002\n\u0002\u0018\u0002\n\u0002\u0018\u0002\n\u0002\b\u0002\u001a\u0019\u0010\u0000\u001a\u00020\u00012\f\u0010\u0002\u001a\b\u0012\u0004\u0012\u00020\u00040\u0003¢\u0006\u0002\u0010\u0005\u001a7\u0010\u0006\u001a\u00020\u00012\u0006\u0010\u0007\u001a\u00020\b2\u0006\u0010\t\u001a\u00020\b2\u001c\u0010\n\u001a\u0018\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u000bj\u0002`\fH\u0086\b*.\u0010\r\"\u0014\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u000b2\u0014\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b\u0012\u0004\u0012\u00020\b0\u000b¨\u0006\u000e"},
       d2 = {
        "main", "", "args", "", "", "([Ljava/lang/String;)V", "printSum", "a", "", "b", "block", "Lkotlin/Function2;", "Lcom/mikyou/kotlin/lambda/high/SumAlias;", "SumAlias", "production sources for module Lambda_main"}
    )
    public final class SumHighFuntionKt {
        
       public static final void printSum(int a, int b, @NotNull Function2 block) {
        
          Intrinsics.checkParameterIsNotNull(block, "block");
          int var4 = ((Number)block.invoke(a, b)).intValue();
          System.out.println(var4);
       }
    
       public static final void main(@NotNull String[] args) {
        
          Intrinsics.checkParameterIsNotNull(args, "args");
          //下面调用地方直接是把传入block替换到该调用处执行，根本就不需要了Function2实例对象，这样会降低类创建和生成的开销。
          byte a$iv = 4;
          int b$iv = 5;
          int var4 = a$iv + b$iv;
          System.out.println(var4);
       }
    }

### 七、使用lambda表达式需要注意哪些问题 ###

*  1、在使用proguard的时候需要注意不要将@Metadata注解中信息给混淆了，否则会有异常抛出。
 *  2、在使用高阶函数时，尽量去使用inline函数，降低类生成和类的实例创建的开销。关于内联函数，我们会在接下来博客一一详细介绍。

![1635c3fb0ba21ec1_w_430_h_430_f_jpeg_s_39536][]

**欢迎关注Kotlin开发者联盟，这里有最新Kotlin技术文章，每周会不定期翻译一篇Kotlin国外技术文章。如果你也喜欢Kotlin，欢迎加入我们~~~**

### Kotlin系列文章，欢迎查看: ###

> Kotlin邂逅设计模式系列:

*  **[当Kotlin完美邂逅设计模式之单例模式(一)][Kotlin]**

> 数据结构与算法系列:

*  **[每周一算法之二分查找(Kotlin描述)][Kotlin 1]**

> 翻译系列：

*  **[\[译\] Kotlin中关于Companion Object的那些事][Kotlin_Companion Object]**
 *  **[\[译\]记一次Kotlin官方文档翻译的PR(内联类)][Kotlin_PR]**
 *  **[\[译\]Kotlin中内联类的自动装箱和高性能探索(二)][Kotlin 2]**
 *  **[\[译\]Kotlin中内联类(inline class)完全解析(一)][Kotlin_inline class]**
 *  **[\[译\]Kotlin的独门秘籍Reified实化类型参数(上篇)][Kotlin_Reified]**
 *  **[\[译\]Kotlin泛型中何时该用类型形参约束?][Kotlin 3]**
 *  **[\[译\] 一个简单方式教你记住Kotlin的形参和实参][_Kotlin]**
 *  **[\[译\]Kotlin中是应该定义函数还是定义属性?][Kotlin 4]**
 *  **[\[译\]如何在你的Kotlin代码中移除所有的!!(非空断言)][Kotlin 5]**
 *  **[\[译\]掌握Kotlin中的标准库函数: run、with、let、also和apply][Kotlin_ run_with_let_also_apply]**
 *  **[\[译\]有关Kotlin类型别名(typealias)你需要知道的一切][Kotlin_typealias]**
 *  **[\[译\]Kotlin中是应该使用序列(Sequences)还是集合(Lists)?][Kotlin_Sequences_Lists]**
 *  **[\[译\]Kotlin中的龟(List)兔(Sequence)赛跑][Kotlin_List_Sequence]**

> 原创系列：

*  **[教你如何完全解析Kotlin中的类型系统][Kotlin 6]**
 *  **[如何让你的回调更具Kotlin风味][Kotlin 7]**
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 *  **[JetBrains开发者日见闻(二)之Kotlin1.3的新特性(Contract契约与协程篇)][JetBrains_Kotlin1.3_Contract]**
 *  **[JetBrains开发者日见闻(一)之Kotlin/Native 尝鲜篇][JetBrains_Kotlin_Native]**
 *  **[教你如何攻克Kotlin中泛型型变的难点(实践篇)][Kotlin 8]**
 *  **[教你如何攻克Kotlin中泛型型变的难点(下篇)][Kotlin 9]**
 *  **[教你如何攻克Kotlin中泛型型变的难点(上篇)][Kotlin 10]**
 *  **[Kotlin的独门秘籍Reified实化类型参数(下篇)][Kotlin_Reified 1]**
 *  **[有关Kotlin属性代理你需要知道的一切][Kotlin 11]**
 *  **[浅谈Kotlin中的Sequences源码解析][Kotlin_Sequences]**
 *  **[浅谈Kotlin中集合和函数式API完全解析-上篇][Kotlin_API_-]**
 *  **[浅谈Kotlin语法篇之lambda编译成字节码过程完全解析][Kotlin_lambda]**
 *  **[浅谈Kotlin语法篇之Lambda表达式完全解析][Kotlin_Lambda]**
 *  **[浅谈Kotlin语法篇之扩展函数][Kotlin 12]**
 *  **[浅谈Kotlin语法篇之顶层函数、中缀调用、解构声明][Kotlin 13]**
 *  **[浅谈Kotlin语法篇之如何让函数更好地调用][Kotlin 14]**
 *  **[浅谈Kotlin语法篇之变量和常量][Kotlin 15]**
 *  **[浅谈Kotlin语法篇之基础语法][Kotlin 16]**

> Effective Kotlin翻译系列

*  **[\[译\]Effective Kotlin系列之考虑使用原始类型的数组优化性能(五)][Effective Kotlin]**
 *  **[\[译\]Effective Kotlin系列之使用Sequence来优化集合的操作(四)][Effective Kotlin_Sequence]**
 *  **[\[译\]Effective Kotlin系列之探索高阶函数中inline修饰符(三)][Effective Kotlin_inline]**
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 *  **[\[译\]Effective Kotlin系列之考虑使用静态工厂方法替代构造器(一)][Effective Kotlin 2]**

> 实战系列:

*  **[用Kotlin撸一个图片压缩插件ImageSlimming-导学篇(一)][Kotlin_ImageSlimming-]**
 *  **[用Kotlin撸一个图片压缩插件-插件基础篇(二)][Kotlin_-]**
 *  **[用Kotlin撸一个图片压缩插件-实战篇(三)][Kotlin_- 1]**
 *  **[浅谈Kotlin实战篇之自定义View图片圆角简单应用][Kotlin_View]**

[BytecodeViewer]: https://bytecodeviewer.com/
[163077d3d55a094e_w_1188_h_755_f_jpeg_s_133209]: https://user-gold-cdn.xitu.io/2018/4/27/163077d3d55a094e?w=1188&h=755&f=jpeg&s=133209
[163077cf2e40f577_w_1176_h_750_f_jpeg_s_547145]: https://user-gold-cdn.xitu.io/2018/4/27/163077cf2e40f577?w=1176&h=750&f=jpeg&s=547145
[16307956d8888bce_w_1241_h_201_f_png_s_25476]: https://user-gold-cdn.xitu.io/2018/4/27/16307956d8888bce?w=1241&h=201&f=png&s=25476
[Link 1]: https://github.com/JetBrains/kotlin/blob/e83f1b138b554209a310d6d04e810dfced4d4d29/core/deserialization/src/descriptors.proto
[1630a4327a4f6daa_w_553_h_1021_f_png_s_94428]: https://user-gold-cdn.xitu.io/2018/4/28/1630a4327a4f6daa?w=553&h=1021&f=png&s=94428
[1630c2bf7d169bec_w_610_h_732_f_png_s_55803]: https://user-gold-cdn.xitu.io/2018/4/28/1630c2bf7d169bec?w=610&h=732&f=png&s=55803
[1630c5d980701d03_w_1684_h_120_f_png_s_54193]: https://user-gold-cdn.xitu.io/2018/4/28/1630c5d980701d03?w=1684&h=120&f=png&s=54193
[1630c69a7284a7e1_w_1600_h_78_f_png_s_33636]: https://user-gold-cdn.xitu.io/2018/4/28/1630c69a7284a7e1?w=1600&h=78&f=png&s=33636
[1635c3fb0ba21ec1_w_430_h_430_f_jpeg_s_39536]: https://user-gold-cdn.xitu.io/2018/5/14/1635c3fb0ba21ec1?w=430&h=430&f=jpeg&s=39536
[Kotlin]: https://blog.csdn.net/u013064109/article/details/89078666
[Kotlin 1]: https://blog.csdn.net/u013064109/article/details/89023937
[Kotlin_Companion Object]: https://blog.csdn.net/u013064109/article/details/89199478
[Kotlin_PR]: https://blog.csdn.net/u013064109/article/details/85180755
[Kotlin 2]: https://blog.csdn.net/u013064109/article/details/84899657
[Kotlin_inline class]: https://blog.csdn.net/u013064109/article/details/84866092
[Kotlin_Reified]: https://blog.csdn.net/u013064109/article/details/83388976
[Kotlin 3]: https://blog.csdn.net/u013064109/article/details/83120352
[_Kotlin]: https://blog.csdn.net/u013064109/article/details/83099581
[Kotlin 4]: https://blog.csdn.net/u013064109/article/details/80344848
[Kotlin 5]: https://blog.csdn.net/u013064109/article/details/80358822
[Kotlin_ run_with_let_also_apply]: https://blog.csdn.net/u013064109/article/details/80387322
[Kotlin_typealias]: https://blog.csdn.net/u013064109/article/details/80444565
[Kotlin_Sequences_Lists]: https://blog.csdn.net/u013064109/article/details/80562009
[Kotlin_List_Sequence]: https://blog.csdn.net/u013064109/article/details/80740230
[Kotlin 6]: https://blog.csdn.net/u013064109/article/details/88985474
[Kotlin 7]: https://blog.csdn.net/u013064109/article/details/86695094
[Jetbrains_Kotlin1.3_inline class]: https://blog.csdn.net/u013064109/article/details/84837918
[JetBrains_Kotlin1.3_Contract]: https://blog.csdn.net/u013064109/article/details/84782206
[JetBrains_Kotlin_Native]: https://blog.csdn.net/u013064109/article/details/84729814
[Kotlin 8]: https://blog.csdn.net/u013064109/article/details/84504847
[Kotlin 9]: https://blog.csdn.net/u013064109/article/details/84060626
[Kotlin 10]: https://blog.csdn.net/u013064109/article/details/83869716
[Kotlin_Reified 1]: https://blog.csdn.net/u013064109/article/details/83507076
[Kotlin 11]: https://blog.csdn.net/u013064109/article/details/82794410
[Kotlin_Sequences]: https://blog.csdn.net/u013064109/article/details/80588034
[Kotlin_API_-]: https://blog.csdn.net/u013064109/article/details/80275942
[Kotlin_lambda]: https://blog.csdn.net/u013064109/article/details/80139556
[Kotlin_Lambda]: https://blog.csdn.net/u013064109/article/details/80088158
[Kotlin 12]: https://blog.csdn.net/u013064109/article/details/79968846
[Kotlin 13]: https://blog.csdn.net/u013064109/article/details/79887528
[Kotlin 14]: https://blog.csdn.net/u013064109/article/details/79503709
[Kotlin 15]: https://blog.csdn.net/u013064109/article/details/79296502
[Kotlin 16]: https://blog.csdn.net/u013064109/article/details/77843579
[Effective Kotlin]: https://blog.csdn.net/u013064109/article/details/84996951
[Effective Kotlin_Sequence]: https://blog.csdn.net/u013064109/article/details/84981570
[Effective Kotlin_inline]: https://blog.csdn.net/u013064109/article/details/84948769
[Effective Kotlin 1]: https://blog.csdn.net/u013064109/article/details/82121020
[Effective Kotlin 2]: https://blog.csdn.net/u013064109/article/details/81916446
[Kotlin_ImageSlimming-]: https://blog.csdn.net/u013064109/article/details/80850992
[Kotlin_-]: https://blog.csdn.net/u013064109/article/details/80879296
[Kotlin_- 1]: https://blog.csdn.net/u013064109/article/details/81814643
[Kotlin_View]: https://blog.csdn.net/u013064109/article/details/80102036