【2021-11-24】【Kotlin】Scope Functions：let、with、run、apply、also 的区别；关于 receiver 的一些解释说明：receiver 到底是什么？

Kotlin 的 Scope Functions

Kotlin 的这几个语法糖的用法都是比较相似的：

let

The context object is available as an argument (it). The return value is the lambda result.

val str: String? = "Hello"   
//processNonNullString(str)       // compilation error: str can be null
val length = str?.let {
   
    
    println("let() called on $it")// 'it' refers to 'str: String = "Hello"'
    processNonNullString(it)      // OK: 'it' is not null inside '?.let { }'
    it.length
}

with

A non-extension function:
the context object is passed as an argument,
but inside the lambda, it’s available as a receiver (this). The return value is the lambda result.

val numbers = mutableListOf("one", "two", "three")
val firstAndLast = with(numbers) {
   
   
    "The first element is ${
     
     <