Defer {.en}

推迟 {.zh}

::: {.en} Defer is used to ensure that a function call is performed later in a program’s execution, usually for purposes of cleanup. defer is often used where e.g. ensure and finally would be used in other languages. :::

::: {.zh}

Defer用于确保稍后在程序执行中执行函数调用，通常用于清理。经常使用defer，例如.ensure和finally将用于其他语言。

:::

package main
import "fmt"
import "os"

::: {.en} Suppose we wanted to create a file, write to it, and then close when we’re done. Here’s how we could do that with defer. :::

::: {.zh}

假设我们想要创建一个文件，写入它，然后在我们完成时关闭。这就是我们用defer来做到这一点的方法。

:::

func main() {

::: {.en} Immediately after getting a file object with createFile, we defer the closing of that file with closeFile. This will be executed at the end of the enclosing function (main), after writeFile has finished. :::

::: {.zh}

在使用createFile获取文件对象后，我们立即将该文件的关闭推迟到closeFile。在writeFile完成之后，这将在封闭函数（main）的末尾执行。

:::

    f := createFile("/tmp/defer.txt")
    defer closeFile(f)
    writeFile(f)
}
func createFile(p string) *os.File {
    fmt.Println("creating")
    f, err := os.Create(p)
    if err != nil {
        panic(err)
    }
    return f
}
func writeFile(f *os.File) {
    fmt.Println("writing")
    fmt.Fprintln(f, "data")
}
func closeFile(f *os.File) {
    fmt.Println("closing")
    f.Close()
}

::: {.en} Running the program confirms that the file is closed after being written. :::

::: {.zh}

运行程序确认文件在写入后关闭。

:::

$ go run defer.go
creating
writing
closing