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53 lines
1.1 KiB
Go
53 lines
1.1 KiB
Go
// _Defer_ is used to ensure that a function call is
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// performed later in a program's execution, usually for
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// purposes of cleanup. `defer` is often used where e.g.
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// `ensure` and `finally` would be used in other languages.
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package main
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import (
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"fmt"
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"os"
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)
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// Suppose we wanted to create a file, write to it,
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// and then close when we're done. Here's how we could
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// do that with `defer`.
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func main() {
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// Immediately after getting a file object with
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// `createFile`, we defer the closing of that file
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// with `closeFile`. This will be executed at the end
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// of the enclosing function (`main`), after
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// `writeFile` has finished.
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f := createFile("/tmp/defer.txt")
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defer closeFile(f)
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writeFile(f)
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}
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func createFile(p string) *os.File {
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fmt.Println("creating")
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f, err := os.Create(p)
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if err != nil {
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panic(err)
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}
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return f
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}
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func writeFile(f *os.File) {
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fmt.Println("writing")
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fmt.Fprintln(f, "data")
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}
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func closeFile(f *os.File) {
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fmt.Println("closing")
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err := f.Close()
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// It's important to check for errors when closing a
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// file, even in a deferred function.
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if err != nil {
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fmt.Fprintf(os.Stderr, "error: %v\n", err)
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os.Exit(1)
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}
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}
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