Kotlin also let 内联扩展函数

Posted 2022-01-03 安果移不动

首先 also 英语是而且的意思 let是允许

also的源码是这样的

@kotlin.internal.InlineOnly
@SinceKotlin("1.1")
public inline fun <T> T.also(block: (T) -> Unit): T 
    contract 
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    
    block(this)
    return this

 retrun this操作对象后返回对象。

package com.yzdzy.kotlin.temp

fun main() 
   val res= "Also".also 
        println(it.length)
        it.replace("Also","狗蛋")
    
    println(res)

 输出

4
Also

这点要是切换到let。。。就会返回最后一行的结果

let 源码

/**
 * Calls the specified function [block] with `this` value as its argument and returns its result.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#let).
 */
@kotlin.internal.InlineOnly
public inline fun <T, R> T.let(block: (T) -> R): R 
    contract 
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    
    return block(this)

代码示例

package com.yzdzy.kotlin.temp

fun main() 
   val res= "let".let 
        println(it.length)
        it.replace("let","狗蛋")
    
    println(res)

输出

3
狗蛋