io/ioutil の非推奨化について

package ioutil

import (
	"io"
	"io/fs"
	"os"
	"sort"
)

// ReadAll reads from r until an error or EOF and returns the data it read.
// A successful call returns err == nil, not err == EOF. Because ReadAll is
// defined to read from src until EOF, it does not treat an EOF from Read
// as an error to be reported.
//
// As of Go 1.16, this function simply calls io.ReadAll.
func ReadAll(r io.Reader) ([]byte, error) {
	return io.ReadAll(r)
}

// ReadFile reads the file named by filename and returns the contents.
// A successful call returns err == nil, not err == EOF. Because ReadFile
// reads the whole file, it does not treat an EOF from Read as an error
// to be reported.
//
// As of Go 1.16, this function simply calls os.ReadFile.
func ReadFile(filename string) ([]byte, error) {
	return os.ReadFile(filename)
}

// WriteFile writes data to a file named by filename.
// If the file does not exist, WriteFile creates it with permissions perm
// (before umask); otherwise WriteFile truncates it before writing, without changing permissions.
//
// As of Go 1.16, this function simply calls os.WriteFile.
func WriteFile(filename string, data []byte, perm fs.FileMode) error {
	return os.WriteFile(filename, data, perm)
}

// NopCloser returns a ReadCloser with a no-op Close method wrapping
// the provided Reader r.
//
// As of Go 1.16, this function simply calls io.NopCloser.
func NopCloser(r io.Reader) io.ReadCloser {
	return io.NopCloser(r)
}

// Discard is an io.Writer on which all Write calls succeed
// without doing anything.
//
// As of Go 1.16, this value is simply io.Discard.
var Discard io.Writer = io.Discard

// ReadDir reads the directory named by dirname and returns
// a list of fs.FileInfo for the directory's contents,
// sorted by filename. If an error occurs reading the directory,
// ReadDir returns no directory entries along with the error.
//
// As of Go 1.16, os.ReadDir is a more efficient and correct choice:
// it returns a list of fs.DirEntry instead of fs.FileInfo,
// and it returns partial results in the case of an error
// midway through reading a directory.
func ReadDir(dirname string) ([]fs.FileInfo, error) {
    f, err := os.Open(dirname)
    if err != nil {
        return nil, err
    }
    list, err := f.Readdir(-1)
    f.Close()
    if err != nil {
        return nil, err
    }
    sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() })
    return list, nil
}

// A FileInfo describes a file and is returned by Stat.
type FileInfo interface {
    Name() string       // base name of the file
    Size() int64        // length in bytes for regular files; system-dependent for others
    Mode() FileMode     // file mode bits
    ModTime() time.Time // modification time
    IsDir() bool        // abbreviation for Mode().IsDir()
    Sys() interface{}   // underlying data source (can return nil)
}

// A FileMode represents a file's mode and permission bits.
// The bits have the same definition on all systems, so that
// information about files can be moved from one system
// to another portably. Not all bits apply to all systems.
// The only required bit is ModeDir for directories.
type FileMode uint32

package os

import (
	"io/fs"
	"syscall"
)

// A FileInfo describes a file and is returned by Stat and Lstat.
type FileInfo = fs.FileInfo

// A DirEntry is an entry read from a directory
// (using the ReadDir function or a File's ReadDir method).
type DirEntry = fs.DirEntry

// ReadDir reads the named directory,
// returning all its directory entries sorted by filename.
// If an error occurs reading the directory,
// ReadDir returns the entries it was able to read before the error,
// along with the error.
func ReadDir(name string) ([]DirEntry, error) {
    f, err := Open(name)
    if err != nil {
        return nil, err
    }
    defer f.Close()

    dirs, err := f.ReadDir(-1)
    sort.Slice(dirs, func(i, j int) bool { return dirs[i].Name() < dirs[j].Name() })
    return dirs, err
}

// A DirEntry is an entry read from a directory
// (using the ReadDir function or a ReadDirFile's ReadDir method).
type DirEntry interface {
    // Name returns the name of the file (or subdirectory) described by the entry.
    // This name is only the final element of the path (the base name), not the entire path.
    // For example, Name would return "hello.go" not "/home/gopher/hello.go".
    Name() string

    // IsDir reports whether the entry describes a directory.
    IsDir() bool

    // Type returns the type bits for the entry.
    // The type bits are a subset of the usual FileMode bits, those returned by the FileMode.Type method.
    Type() FileMode

    // Info returns the FileInfo for the file or subdirectory described by the entry.
    // The returned FileInfo may be from the time of the original directory read
    // or from the time of the call to Info. If the file has been removed or renamed
    // since the directory read, Info may return an error satisfying errors.Is(err, ErrNotExist).
    // If the entry denotes a symbolic link, Info reports the information about the link itself,
    // not the link's target.
    Info() (FileInfo, error)
}