go中的"defer"是什么意思?

问题描述

限时删除！！

golang的文档说:

golang's documentation says this:

这使我感到困惑.

问题:已评估"是否意味着该值已经已知?我只是不明白为什么两个例子打印的不同.这使我感到困惑.

Question: Does "evaluated" mean that the value is already known? I just don't understand why two examples print different. This confuse me.

我下面有两个例子:

 //It prints 0.
 func deferA() {
     i := 0
     defer fmt.Println(i)
     i++
     return
 }

 //It prints 1.
 func deferB() {
      i := 0
      defer func() {
          fmt.Println(i)
      }()
      i++
      return
 }

推荐答案

defer 采用一个函数，因此 fmt.Println(i)是一个函数，其参数 i 评估为 0 .

defer take a function, so fmt.Println(i) is a function and its argument i is evaluated as 0 when the defer statement is evaluated.

defer func(){fmt.Println(i)} ， func(){fmt.Println(i)} 不带参数，并且闭包，因此 i 不会被评估，但会被闭包关闭.

defer func() { fmt.Println(i) }, the func() { fmt.Println(i) } take no argument and its a closure, so i is not evaluated but close over by the closure.

您可以在 https://gobyexample.com/closures

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