覆盖全局变量

Question

我想知道为什么以下代码中没有警告或错误允许我覆盖全局变量。// You can edit this code!// Click here and start typing.package mainimport "fmt"type MyStruct struct {    MyInt uint32}func (s *MyStruct) MyMethod() {    fmt.Println(s.MyInt)}var theStruct MyStructfunc main() {    // Override the above global variable    // I would expect some kind of warning or error here?    theStruct := MyStruct {        MyInt: 42,    }    // Outputs 42    theStruct.MyMethod()    // Outputs 0    UseMyStruct()}func UseMyStruct() {    theStruct.MyMethod()}

Answer 1

变量可以隐藏父作用域中的其他变量。在您的示例中，范围层次结构如下所示：

global (scope)

├── theStruct (variable)

└── main (scope)

    └── theStruct (variable)

像这样的阴影通常是通过以下方式完成的err：

package main

import (

    "io/ioutil"

    "log"

)

func main() {

    f, err := ioutil.TempFile("", "")

    if err != nil {

        log.Fatal(err)

    }

    defer f.Close()

    // This err shadows the one above, it is technically in its

    // own scope within the "if".

    if _, err := f.Write([]byte("hello world\n")); err != nil {

        log.Fatal(err)

    }

    if true {

        // We can even shadow with different types!

        err := 3

        log.Println(err)

    }

}