Generative Programming in Go

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Generative Programming in Go - GoCon 2015 summer - @monochromegane

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MIYAKE Yusuke (@monochromegane)

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GMO Pepabo, Inc.

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♕ 3 GitHub Awards Go ranking in Japan :)

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Generative Programming

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ੜ੒తͳ Programming

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Generator + Template parse generate Parser Your App Generated Code AST Code use

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Attention, please.

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✘ Generics Meta programming Dynamic generation

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parse Parser AST Code Go provides

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Generator + Template generate Your App Generated Code use We implement

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argen ActiveRecord Generator

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GoͰDataMapperͰ͸ͳ͘ ActiveRecordϥΠΫʹ DBૢ࡞͢Δ

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by Generative programming

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ߏ଄ମʹ`+AR`ϚʔΧʔΛ͚ͭΔ //+AR type User struct { Id int Name string Age int }

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ੜ੒͢Δ $ argen main.go $ tree . !"" main.go #"" main_gen.go

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ߏ଄ମʹARϥΠΫͳϝιου͕ ௥Ճ͞ΕΔ db, _ := sql.Open("sqlite3", "foo.db") Use(db) u := User{Name: "test", Age: 20} u.Save() //// INSERT INTO users (name, age) VALUES (?, ?); [test 20] User{}.Where("name", "test").And("age", ">", 20).Query() //// SELECT users.id, users.name, users.age FROM users WHERE name = ? AND age > ?; [test 20]

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Generative Programming ࢖͍υίϩ

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Case.1 Generics

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೚ҙͷߏ଄ମʹڞ௨ͷϝιου Λ࣋ͨͤͭͭɺݸʑͷܕΛѻ͏ var u User u = User{}.First() var h Hoge h = Hoge{}.First()

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೚ҙͷߏ଄ମʹڞ௨ͷϝιου Λ࣋ͨͤͭͭɺݸʑͷܕΛѻ͏ var u User u = User{}.First() var h Hoge h = Hoge{}.First() • Ωϟετͨ͘͠ͳ͍ • Genericsͷग़൪

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ᵆᴸᴸᴸᴸᴸᴸᴸᴸᴸᴸᴸᴸᴸᵪᴸᴸᵊ ᴺwhy no generics golangɹ ᴺݕࡧᴺ ᵎᴸᴸᴸᴸᴸᴸᴸᴸᴸᴸᴸᴸᴸᵲᴸᴸᵒ

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Let’s generate !

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ߏ଄ମʹରͯ͠ݸʑͷܕΛѻ͏ ڞ௨ͷϝιουΛੜ੒

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func (m User) First() (*User, error) { return m.newRelation().First() } func (r *UserRelation) First() (*User, error) { return r.Order("id", "ASC").Limit(1).QueryRow() } func (r *UserRelation) QueryRow() (*User, error) { row := &User{} err := r.Relation.QueryRow( row.fieldPtrsByName( r.Relation.GetColumns())...) if err != nil { return nil, err } return row, nil }

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see also: clipperhouse/gen // +gen slice:"All" type Person struct { Name string Present bool } gang := PersonSlice { {"Alice", true}, {"Bob", false}, {"Carly", true}, } here := func(p Person) bool { return p.Present } gang.All(here) // => false, Bob didn't make it

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Case.2 Performance

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ϦϑϨΫγϣϯΛ࢖ͬͨ൚༻ੑ ͸ύϑΥʔϚϯεͱҾ͖׵͑ // Useful! but... var u User db.First(&u)

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ϕϯνϚʔΫ // read SomeFunc(s.F) SomeFunc(reflect.ValueOf(s).FieldByName("F").Int()) // write s.F = 100 reflect.ValueOf(&s).Elem().FieldByName("F").SetInt(100) $ go test -benchmem -bench . • Mac OSX(10.10.3) • CPU: 2.5GHz Core i5(2Core) • Memory: 8GB • Go: 1.4.2

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ߏ଄ମϑΟʔϧυʹର͢ΔΞΫηε time Alloced Bytes Allocs read field 0.38 ns 0 B 0 allocs reflect 246 ns 16 B 2 allocs write field 0.36 ns 0 B 0 allocs reflect 199 ns 8 B 1 allocs

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ෳ਺ͷߏ଄ମϑΟʔϧυʹର͢ΔΞΫηε time Alloced Bytes Allocs read field 0.36 ns 0 B 0 allocs reflect 583 ns 88 B 2 allocs write field 0.37 ns 0 B 0 allocs reflect 277 ns 8 B 1 allocs

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Let’s generate !

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ߏ଄ମʹରͯ͠ϑΟʔϧυ৘ใ औಘ༻ϝιουΛੜ੒

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func (m *User) fieldValueByName(name string) interface{} { switch name { case "id", "users.id": return m.Id case "name", "users.name": return m.Name case "age", "users.age": return m.Age default: return "" } } func (m *User) fieldPtrByName(name string) interface{} { switch name { case "id", "users.id": return &m.Id case "name", "users.name": return &m.Name case "age", "users.age": return &m.Age default: return nil } }

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see also: pquerna/ffjson //go:generate ffjson $GOFILE type Foo struct { Bar string } f := Foo{"bar"} b, _ := json.Marshal(f) fmt.Printf("%s\n", string(b)) // => {"Bar":"bar"} https://github.com/pquerna/ffjson

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Case.3 DSL

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೚ҙͷߏ଄ମͷڞ௨ϝιου͸ هड़಺༰͕৑௕ʹͳΓ͕ͪ // far from the DSL... func (u *User) BeforeUpdate() (err error) { if u.Name != "abc"{ return fmt.Errorf("%s is invalid name.", u.Name) } if u.Age > 20 { return fmt.Errorf("%d is invalid age.", u.Age) } return nil }

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Let’s generate !

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ϝιου໊/ίϝϯτ/λά͔Β ఆٛΛิ׬ͯ͠ੜ੒

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func (u User) validatesName() ar.Rule { return ar.MakeRule().Format().With("abc").OnCreate() } func (u User) validatesAge() ar.Rule { return ar.MakeRule().Numericality().OnlyInteger().LessThan(20) } rules := map[string]*ar.Validation{ "name": m.validatesName().Rule(), "age": m.validatesAge().Rule(), } for name, rule := range rules { if ok, errs := ar.NewValidator(rule).On(on).IsValid(m.fieldValueByName(name)); !ok { result = false errors.SetErrors(name, errs) } } >

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Case. Bad

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ͳΜͰ΋Generate

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• ϝιουͷڞ௨Խɺଟଶੑͷ࣮ݱͳͲ͸ߏ଄ମͷຒࠐ (ҕৡ)΍interfaceΛ࢖ͬͯ΍Δ΂͖ • http://go-talks.appspot.com/github.com/lestrrat/ go-slides/2014-yapcasia-go-for-perl-mongers/ main.slide#27 • http://blog.monochromegane.com/blog/ 2014/03/23/struct-implementaion-patterns-in- golang/ • Generate͸࣮૷ଆ΋ར༻ଆ΋Ұख͔͔ؒΔ෼ɺෳࡶ ʹͳΓ͕ͪɻGenerateͰ΍Δཧ༝͕આ໌Ͱ͖ͳ͍ͷ Ͱ͋Ε͹࢖͏΂͖Ͱ͸ͳ͍

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Tips

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ίϚϯυϥΠϯ/go generate ͷ྆ํʹରԠ͢Δ

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from := os.Getenv("GOFILE") if from == "" { if len(args) > 0 { from = args[0] } else { os.Exit(1) } } $ argen main.go // go:generate argen

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deﬁneΛ࢖ͬͯ templateΛ෼ׂ؅ཧ͢Δ

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{{template "Relation" .}} {{define "Relation"}} type {{.Name}}Relation struct { src *{{.Name}} *ar.Relation } {{end}} func (t Template) toDefine() string { return fmt.Sprintf("{{define \"%s\"}}%s{{end}}\n", t.Name, t.Text) } var relation = &Template{ Name: "Relation", Text: ` type {{.Name}}Relation struct { src *{{.Name}} *ar.Relation }`

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templateͰ ࣗಈ੔ܗͱ ΦʔτΠϯϙʔτ

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func writeWithFormat(file, template string, structs structs) ([]byte, error) { var b bytes.Buffer w := bufio.NewWriter(&b) write(w, template, structs) w.Flush() formatted, err := imports.Process(file, b.Bytes(), nil) if err != nil { return nil, err } return formatted, nil } func write(w io.Writer, tplText string, structs structs) error { t := template.New("t") t.Funcs(template.FuncMap{}) tpl := template.Must(t.Parse(tplText)) if err := tpl.Execute(w, structs); err != nil { return err } return nil }

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ςετ͸ੜ੒෺ʹ ରͯ͠ߦ͏

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//go:generate go run ../cmd/argen/main.go package tests import "github.com/monochromegane/argen" //+AR type User struct { Name string Age int } $ go generate && go test ./...

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એ఻ ϖύϘͰ͸ΤϯδχΞΛืू͍ͯ͠·͢ɻ ڞʹαʔϏεΛੜΈग़͠ҭͯͯ͘ΕΔ৽͍͠஥ؒ Λ଴͍ͬͯ·͢ɻ http://pepabo.com/recruit/career/engineer/

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͓ΘΓ