延迟功能不恢复

Question

所以，我一直在go中摆弄，发现下面的函数恢复成功了

package main

import (
    "fmt"
)

func a() {  
    defer func(){
        if r := recover(); r != nil {
            fmt.Println("Recovered", r)
        }
    }()
    n := []int{5, 7, 4}
    fmt.Println(n[3])
    fmt.Println("normally returned from a")
}

func main() {  
    a()
    fmt.Println("normally returned from main")
}

但这不是

package main

import (
    "fmt"
)

func r() {  
    if r := recover(); r != nil {
        fmt.Println("Recovered", r)
    }
}

func a() {  
    defer func(){
        r()
    }()
    n := []int{5, 7, 4}
    fmt.Println(n[3])
    fmt.Println("normally returned from a")
}

func main() {  
    a()
    fmt.Println("normally returned from main")
}

谁能解释一下为什么？我一直在寻找答案，但没有找到任何我能完全理解的东西。谢谢。

Answer 1

恢复调用只会在直接从延迟函数调用时停止恐慌。这是来自 recover documentation 的相关文本：

Executing a call to recover inside a deferred function (but not any function called by it) stops the panicking sequence by restoring normal execution and retrieves the error value passed to the call of panic.

延迟功能不恢复

defer func not recover

recover

go

panic

deferred