Gtg12
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This document discusses techniques for writing domain-specific languages (DSLs) in Go. It begins by providing an example of a DSL for service configuration in Go using self-referential functions. It then compares DSLs in Ruby, noting issues like lack of type safety and syntax errors. The document goes on to discuss using code generation in Go with go:generate to reduce boilerplate like error handling. It provides an example of a code generator that automatically adds error handling based on error variable names. In summary, the document explores writing DSLs in Go and techniques like code generation to improve developer experience.
Gtg12
- 1. Happy Programming with Go Compiler GTG 12 poga
- 3. Today • Tricks to write DSL in Go • code generation with GO GENERATE
- 4. DSL in Go s.Config( LogLevel(WARN), Backend(S3{ Key: "API_KEY", Secret: "SUPER SECRET", }), AfterComplete(func() { fmt.Println("service ready") }), ) Do(With{A: "foo", B: 123})
- 6. Ruby • DSL! • Slow • Error-prone
- 7. DSL in Ruby
- 8. DSL in Ruby validates :name, presence: true validate :name, presence: true validates :name, presense: true Which is correct?
- 9. DSL in Ruby validates :points, numericality: true validates :points, numericality: { only: “integer” } validates :points, numericality: { only_integer: true } Which is correct?
- 10. DSL in Ruby • String/symbol + Hash everywhere • lack of “Syntax Error” • everything is void* • anything is ok for ruby interpreter • Need a lot of GOOD documentation
- 11. DSL in Ruby • String/symbol + Hash everywhere • lack of “Syntax Error” • everything is void* • anything is ok for ruby interpreter • Need a lot of GOOD documentation • and memorization
- 12. Go • Fast • Small Footprint
- 13. Go • Fast • Small Footprint • Verbose • sort • if err != nil • if err != nil • if err != nil
- 15. Named Parameter type With struct { A string B int } func main() { Do(With{A: "foo", B: 123}) } func Do(p With) { … }
- 16. Named Parameter • Error when • mistype parameter name • incorrect parameter type
- 17. Configuration s.Config( LogLevel(WARN), Backend(S3{ Key: "API_KEY", Secret: "SUPER SECRET", }), AfterComplete(func() { fmt.Println("service ready") }), ) type Service struct { ErrorLevel int AWSKey string AWSSecret string AfterHook func() } https://gist.github.com/poga/bf0534486199c8e778cb
- 18. Configuration • Self-referential Function type option func(*Service) func (s *Service) Config(opts ...option) { for _, opt := range opts { opt(s) } } func LogLevel(level int) option { return func(s *Service) { s.ErrorLevel = level } } http://commandcenter.blogspot.com.au/2014/01/self-referential-functions-and-design.html
- 19. Struct Tag type Person struct { FirstName string `json:"first_name"` LastName string `json:"last_name"` MiddleName string `json:"middle_name,omitempty"` }
- 20. Struct Tag • Anti-Pattern • String-typing • No compile time checking • 6 month old bug in KKTIX production, no one noticed • based on reflect • slow • Don’t use it as DSL
- 21. Vanilla Go • Sometimes it’s not enough • We need to go deeper
- 22. Code Generation WOW So Rails Much Magic
- 23. Error Handling in Go • Extremely Verbose • We already have 3 official error handling patterns • https://blog.golang.org/errors-are-values • checking error is fine. But I’m lazy to type • Messy control flow
- 24. Error Handler Generation • go get github.com/poga/autoerror • just a demo, don’t use it in production
- 25. Auto Error • Add error checking function based on the name of error variable • Hide error checking from control flow
- 26. //go:generate autoerror -i simple.go -t AutoError -o test.go type AutoError error var e AutoError var e2 AutoError func Test() { e = doSomething() e2 = doSomething() } func doSomething() error { return errors.New("an error") } func handleError2(e2 error) { if e2 != nil { panic(e) } } func handleError(e error) { if e != nil { panic(e) } }
- 27. //go:generate autoerror -i simple.go -t AutoError -o test.go type AutoError error var e AutoError var e2 AutoError func Test() { e = doSomething() e2 = doSomething() } func doSomething() error { return errors.New("an error") } func handleError2(e2 error) { if e2 != nil { panic(e) } } func handleError(e error) { if e != nil { panic(e) } }
- 28. //go:generate autoerror -i simple.go -t AutoError -o test.go type AutoError error var e AutoError var e2 AutoError func Test() { e = doSomething() e2 = doSomething() handleError2(e2) } func doSomething() error { return errors.New("an error") } func handleError2(e2 error) { if e2 != nil { panic(e) } } func handleError(e error) { if e != nil { panic(e) } }
- 29. //go:generate autoerror -i simple.go -t AutoError -o test.go type AutoError error var e AutoError var e2 AutoError func Test() { e = doSomething() e2 = doSomething() handleError2(e2) } func doSomething() error { return errors.New("an error") } func handleError2(e2 error) { if e2 != nil { panic(e) } } func handleError(e error) { if e != nil { panic(e) } }
- 30. //go:generate autoerror -i simple.go -t AutoError -o test.go type AutoError error var e AutoError var e2 AutoError func Test() { e = doSomething() handleError(e) e2 = doSomething() handleError2(e2) } func doSomething() error { return errors.New("an error") } func handleError2(e2 error) { if e2 != nil { panic(e) } } func handleError(e error) { if e != nil { panic(e) } }
- 31. What is Go Generate • shell scripting in go $ go generate //go:generate echo 'hello from go generate' hello from go generate
- 32. go generate • execute a ruby script • integrate with code gen tools • yacc, protocol buffer,… etc //go:generate ruby gen.rb //go:generate codecgen -o values.generated.go file1.go file2.go file3.go
- 33. go generate • go get won’t execute ‘go generate’ for you • generate before publish
- 34. type checking placeholder json.have( pair{Key: “FirstName”, From: “first_name”}, pair{Key: “FirstName”, From: “first_name”}, pair{Key: “MiddleName”, From: “middle_name”, OmitEmpty: true}) type Person struct { FirstName string `json:"first_name"` LastName string `json:"last_name"` MiddleName string `json:"middle_name,omitempty"` }
- 35. person.have( string{Key: “FirstName”, From: “first_name”}, string{Key: “FirstName”, From: “first_name”}, string{Key: “MiddleName”, From: “middle_name”, OmitEmpty: true}) type Person struct { FirstName string `json:"first_name"` LastName string `json:"last_name"` MiddleName string `json:"middle_name,omitempty"` } func (p Person) have(pairs pair…) { panic(“run go generate before use this file”) }
- 36. Recap • DSL • Named Parameter • Configuration • Code Generation • type checking placeholder
- 37. Thank you