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