Functional options are a method of implementing clean/eloquent APIs in Go. Options implemented as a function set the state of that option.
package file
type Options struct {
UID int
GID int
Flags int
Contents string
Permissions os.FileMode
}
type Option func(*Options)
func UID(userID int) Option {
return func(args *Options) {
args.UID = userID
}
}
func GID(groupID int) Option {
return func(args *Options) {
args.GID = groupID
}
}
func Contents(c string) Option {
return func(args *Options) {
args.Contents = c
}
}
func Permissions(perms os.FileMode) Option {
return func(args *Options) {
args.Permissions = perms
}
}
package file
func New(filepath string, setters ...Option) error {
// Default Options
args := &Options{
UID: os.Getuid(),
GID: os.Getgid(),
Contents: "",
Permissions: 0666,
Flags: os.O_CREATE | os.O_EXCL | os.O_WRONLY,
}
for _, setter := range setters {
setter(args)
}
f, err := os.OpenFile(filepath, args.Flags, args.Permissions)
if err != nil {
return err
} else {
defer f.Close()
}
if _, err := f.WriteString(args.Contents); err != nil {
return err
}
return f.Chown(args.UID, args.GID)
}
emptyFile, err := file.New("/tmp/empty.txt")
if err != nil {
panic(err)
}
fillerFile, err := file.New("/tmp/file.txt", file.UID(1000), file.Contents("Lorem Ipsum Dolor Amet"))
if err != nil {
panic(err)
}