为什么golang文件结构设计是这样的

Question

golang File struct is like this:

type File struct{
    *file
}

and File struct functiona is also design to recive a pointer,why it design like this?

Answer 1

It is explained in the Go os package source code comments.

For example, this is safe:

package main

import "os"

func main() {
    f, err := os.Create("/tmp/atestfile")
    if err != nil {
        *f = os.File{}
    }
    // finalizer runs
}

Package os

go/src/os/types.go:

// File represents an open file descriptor.
type File struct {
  *file // os specific
}

go/src/os/file_plan9.go:

// file is the real representation of *File.
// The extra level of indirection ensures that no clients of os
// can overwrite this data, which could cause the finalizer
// to close the wrong file descriptor.
type file struct {
  fd      int
  name    string
  dirinfo *dirInfo // nil unless directory being read
}

go/src/os/file_unix.go:

// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris

// file is the real representation of *File.
// The extra level of indirection ensures that no clients of os
// can overwrite this data, which could cause the finalizer
// to close the wrong file descriptor.
type file struct {
  pfd      poll.FD
  name     string
  dirinfo  *dirInfo // nil unless directory being read
  nonblock bool     // whether we set nonblocking mode
}

go/src/os/file_windows.go:

// file is the real representation of *File.
// The extra level of indirection ensures that no clients of os
// can overwrite this data, which could cause the finalizer
// to close the wrong file descriptor.
type file struct {
  pfd     poll.FD
  name    string
  dirinfo *dirInfo // nil unless directory being read
}