Go for Javaneros

An overview of the Go programming language from the point of view of a seasoned Java developer.
golang, java

1. Go for Javaneros (Javaïstes?) #go4java Francesc Campoy Gopher and Developer Advocate Google
2. What is Go? Go is an open-source programming language created at Google, to solve Google-scale problems.
3. Who uses Go? Google: YouTube dl.google.com Others: dotCloud (Docker) SoundCloud Canonical CloudFlare Mozilla ... golang.org/wiki/GoUsers (http://golang.org/wiki/GoUsers)
4. Who uses Go? Google Trends for golang (http://www.google.com/trends/explore#q=golang)
5. Why Go?
6. Simplicity Minimal design
7. Consistency Orthogonal features By Kenny Louie from Vancouver, Canada CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0) , via Wikimedia Commons
8. Readability “The ratio of time spent reading (code) versus writing is well over 10 to 1 ... (therefore) making it easy to read makes it easier to write.” ― Robert C. Martin
9. Safety Type safety, no buffer overflows, no pointer arithmetic.
10. Built-in concurrency features “In a concurrent world, imperative is the wrong default!” - Tim Sweeney Communicating Sequential Processes - Hoare (1978)
11. Speed
12. Let's dive in
13. Go and Java common aspects Go and Java are object oriented garbage collected statically typed part of the C family
14. Object oriented flavors Go is Object Oriented, but doesn't have the keywords: c l a s s , e x t e n d s , or i m p l e m e n t s .
15. All types are created equal
16. Go types primitive types i n t , u i n t , i n t 8 , u i n t 8 , . . . b o o l , s t r i n g f l o a t 3 2 , f l o a t 6 4 c o m p l e x 6 4 , c o m p l e x 1 2 8 structs s t r u c t { N a m e s t r i n g A g e i n t } slices and arrays [ ] i n t , [ 3 ] s t r i n g , [ ] s t r u c t { N a m e s t r i n g } maps m a p [ s t r i n g ] i n t
17. Kinds of types (continued) pointers * i n t , * P e r s o n functions f u n c ( i n t , i n t ) i n t channels c h a n b o o l interfaces i n t e r f a c e { S t a r t ( ) S t o p ( ) }
18. Type declarations t y p e [ n a m e ] [ s p e c i f i c a t i o n ] P e r s o n is a s t r u c t type. t y p e P e r s o n s t r u c t { n a m e s t r i n g a g e i n t } C e l s i u s is a f l o a t 6 4 type. t y p e C e l s i u s f l o a t 6 4
19. Function declarations f u n c [ n a m e ] ( [ p a r a m s ] ) [ r e t u r n v a l u e ] f u n c [ n a m e ] ( [ p a r a m s ] ) ( [ r e t u r n v a l u e s ] ) A sum function: f u n c s u m ( a i n t , b i n t ) i n t { r e t u r n a + b } A function with multiple returned values: f u n c d i v ( a , b i n t ) ( i n t , i n t ) r e t u r n a / b , a % b } Made clearer by naming the return values: f u n c d i v ( d e n , d i v i n t ) ( q , r e m i n t ) r e t u r n a / b , a % b }
20. Method declarations f u n c ( [ r e c e i v e r ] ) [ n a m e ] ( [ p a r a m s ] ) ( [ r e t u r n v a l u e s ] ) A method on a struct: f u n c ( p P e r s o n ) M a j o r ( ) b o o l { r e t u r n p . a g e > = 1 8 } But also a method on a f l o a t 6 4 : f u n c ( c C e l s i u s ) F r e e z i n g ( ) b o o l { r e t u r n c < = 0 } Constraint: Methods can be defined only on types declared in the same package. / / T h i s w o n ' t c o m p i l e f u n c ( s s t r i n g ) L e n g t h ( ) i n t { r e t u r n l e n ( s ) }
21. Wait, pointers? Use & to obtain the address of a variable. a : = " h e l l o " p : = & a Use * to dereference the pointer. f m t . P r i n t ( * p + " , w o r l d " ) No pointer arithmetic, no pointers to unsafe memory. a : = " h e l l o " p : = & a p + = 4 / / n o , y o u c a n ' t
22. Why pointers? Control what you pass to functions. passing values, no side-effects: f u n c d o u b l e ( x i n t ) { x * = 2 } passing pointers: side-effects possible: f u n c d o u b l e ( x * i n t ) { * x * = 2 } Control your memory layout. compare []Person and []*Person
23. Method declarations on pointers Receivers behave like any other argument. Pointers allow modifying the pointed receiver: f u n c ( p * P e r s o n ) I n c A g e ( ) { p . a g e + + } The method receiver is a copy of a pointer (pointing to the same address). Method calls on nil receivers are perfectly valid (and useful!). f u n c ( p * P e r s o n ) N a m e ( ) s t r i n g { i f p = = n i l { r e t u r n " a n o n y m o u s " } r e t u r n p . n a m e }
24. Interfaces
25. Interfaces An interface is a set of methods. In Java: i n t e r f a c e S w i t c h { v o i d o p e n ( ) ; v o i d c l o s e ( ) ; } In Go: t y p e O p e n C l o s e r i n t e r f a c e { O p e n ( ) C l o s e ( ) }
26. It's all about satisfaction Java interfaces are satisfied explicitly. Go interfaces are satisfied implicitly. Picture by Gorupdebesanez CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) , via Wikimedia Commons (http://commons.wikimedia.org/wiki/File%3ARolling_Stones_09.jpg)
27. Go: implicit satisfaction If a type defines all the methods of an interface, the type satisfies that interface. Benefits: fewer dependencies no type hierarchy organic composition
28. Structural subtyping Think static duck typing, verified at compile time.
29. FuncDraw: an example on interfaces
30. FuncDraw: package parser Package p a r s e provides a parser of strings into functions. f u n c P a r s e ( t e x t s t r i n g ) ( * F u n c , e r r o r ) { . . . } F u n c is a struct type, with an E v a l method. t y p e F u n c s t r u c t { . . . } f u n c ( p * F u n c ) E v a l ( x f l o a t 6 4 ) f l o a t 6 4 { . . . }
31. FuncDraw: package draw Package draw generates images given a function. f u n c D r a w ( f * p a r s e r . F u n c ) i m a g e . I m a g e { f o r x : = s t a r t ; x < e n d ; x + = i n c { y : = f . E v a l ( x ) . . . } } d r a w depends on p a r s e r makes testing hard Let's use an interface instead t y p e E v a l u a b l e i n t e r f a c e { E v a l ( f l o a t 6 4 ) f l o a t 6 4 } f u n c D r a w ( f E v a l u a b l e ) i m a g e . I m a g e { . . . }
32. Inheritance vs composition
33. Inheritance vs composition Lots of articles have been written about the topic. In general, composition is preferred to inheritance. Lets see why.
34. Runner c l a s s R u n n e r { p r i v a t e S t r i n g n a m e ; p u b l i c R u n n e r ( S t r i n g n a m e ) { t h i s . n a m e = n a m e ; } p u b l i c S t r i n g g e t N a m e ( ) { r e t u r n t h i s . n a m e ; } p u b l i c v o i d r u n ( T a s k t a s k ) { t a s k . r u n ( ) ; } p u b l i c v o i d r u n A l l ( T a s k [ ] t a s k s ) { f o r ( T a s k t a s k : t a s k s ) { r u n ( t a s k ) ; } } }
35. RunCounter is-a Runner that counts c l a s s R u n C o u n t e r e x t e n d s R u n n e r { p r i v a t e i n t c o u n t ; p u b l i c R u n C o u n t e r ( S t r i n g m e s s a g e ) { s u p e r ( m e s s a g e ) ; t h i s . c o u n t = 0 ; } @ O v e r r i d e p u b l i c v o i d r u n ( T a s k t a s k ) { c o u n t + + ; s u p e r . r u n ( t a s k ) ; } @ O v e r r i d e p u b l i c v o i d r u n A l l ( T a s k [ ] t a s k s ) { c o u n t + = t a s k s . l e n g t h ; s u p e r . r u n A l l ( t a s k s ) ; } p u b l i c i n t g e t C o u n t ( ) { r e t u r n c o u n t ; } }
36. Let's run and count What will this code print? R u n C o u n t e r r u n n e r = n e w R u n C o u n t e r ( " m y r u n n e r " ) ; T a s k [ ] t a s k s = { n e w T a s k ( " o n e " ) , n e w T a s k ( " t w o " ) , n e w T a s k ( " t h r e e " ) } ; r u n n e r . r u n A l l ( t a s k s ) ; S y s t e m . o u t . p r i n t f ( " % s r a n % d t a s k s \ n " , r u n n e r . g e t N a m e ( ) , r u n n e r . g e t C o u n t ( ) ) ; Of course, this prints: r u n n i n g o n e r u n n i n g t w o r u n n i n g t h r e e m y r u n n e r r a n 6 t a s k s Wait! How many?
37. My runner ran 6 tasks? Six? Inheritance causes: weak encapsulation, tight coupling, surprising bugs.
38. Solution: use composition c l a s s R u n C o u n t e r { p r i v a t e R u n n e r r u n n e r ; p r i v a t e i n t c o u n t ; p u b l i c R u n C o u n t e r ( S t r i n g m e s s a g e ) { t h i s . r u n n e r = n e w R u n n e r ( m e s s a g e ) ; t h i s . c o u n t = 0 ; } p u b l i c v o i d r u n ( T a s k t a s k ) { c o u n t + + ; r u n n e r . r u n ( t a s k ) ; } p u b l i c v o i d r u n A l l ( T a s k [ ] t a s k s ) { c o u n t + = t a s k s . l e n g t h ; r u n n e r . r u n A l l ( t a s k s ) ; } / / c o n t i n u e d o n n e x t s l i d e . . .
39. Solution: use composition (continued) p u b l i c i n t g e t C o u n t ( ) { r e t u r n c o u n t ; } p u b l i c S t r i n g g e t N a m e ( ) { r e t u r n r u n n e r . g e t N a m e ( ) ; } }
40. Solution: use composition (continued) Pros The bug is gone! R u n n e r is completely independent of R u n C o u n t e r . The creation of the R u n n e r can be delayed until (and if) needed. Cons We need to explicitly define the R u n n e r methods on R u n C o u n t e r : p u b l i c S t r i n g g e t N a m e ( ) { r e t u r n r u n n e r . g e t N a m e ( ) ; } This can cause lots of repetition, and eventually bugs.
41. There's no inheritance in Go
42. There's no inheritance in Go Let's use composition directly: t y p e R u n n e r s t r u c t { n a m e s t r i n g } f u n c ( r * R u n n e r ) N a m e ( ) s t r i n g { r e t u r n r . n a m e } f u n c ( r * R u n n e r ) R u n ( t T a s k ) { t . R u n ( ) } f u n c ( r * R u n n e r ) R u n A l l ( t s [ ] T a s k ) { f o r _ , t : = r a n g e t s { r . R u n ( t ) } } All very similar to the Java version.
43. RunCounter R u n C o u n t e r has a R u n n e r field. t y p e R u n C o u n t e r s t r u c t { r u n n e r R u n n e r c o u n t i n t } f u n c N e w R u n C o u n t e r ( n a m e s t r i n g ) * R u n C o u n t e r { r e t u r n & R u n C o u n t e r { r u n n e r : R u n n e r { n a m e } } } f u n c ( r * R u n C o u n t e r ) R u n ( t T a s k ) { r . c o u n t + + r . r u n n e r . R u n ( t ) } f u n c ( r * R u n C o u n t e r ) R u n A l l ( t s [ ] T a s k ) { r . c o u n t + = l e n ( t s ) r . r u n n e r . R u n A l l ( t s ) } f u n c ( r * R u n C o u n t e r ) C o u n t ( ) i n t { r e t u r n r . c o u n t } f u n c ( r * R u n C o u n t e r ) N a m e ( ) s t r i n g { r e t u r n r . r u n n e r . N a m e ( ) }
44. Composition in Go Same pros and cons as the composition version in Java. We also have the boilerplate to proxy methods from R u n n e r . f u n c ( r * R u n C o u n t e r ) N a m e ( ) s t r i n g { r e t u r n r . r u n n e r . N a m e ( ) } But we can remove it!
45. Struct embedding Expressed in Go as unnamed fields in a struct. It is still composition. The fields and methods of the embedded type are defined on the embedding type. Similar to inheritance, but the embedded type doesn't know it's embedded.
46. Example of struct embedding Given a type P e r s o n : t y p e P e r s o n s t r u c t { N a m e s t r i n g } f u n c ( p P e r s o n ) I n t r o d u c e ( ) { f m t . P r i n t l n ( " H i , I ' m " , p . N a m e ) } We can define a type E m p l o y e e embedding P e r s o n : t y p e E m p l o y e e s t r u c t { P e r s o n E m p l o y e e I D i n t } All fields and methods from P e r s o n are available on E m p l o y e e : v a r e E m p l o y e e e . N a m e = " P e t e r " e . E m p l o y e e I D = 1 2 3 4 e . I n t r o d u c e ( )
47. Struct embedding t y p e R u n C o u n t e r 2 s t r u c t { R u n n e r c o u n t i n t } f u n c N e w R u n C o u n t e r 2 ( n a m e s t r i n g ) * R u n C o u n t e r 2 { r e t u r n & R u n C o u n t e r 2 { R u n n e r { n a m e } , 0 } } f u n c ( r * R u n C o u n t e r 2 ) R u n ( t T a s k ) { r . c o u n t + + r . R u n n e r . R u n ( t ) } f u n c ( r * R u n C o u n t e r 2 ) R u n A l l ( t s [ ] T a s k ) { r . c o u n t + = l e n ( t s ) r . R u n n e r . R u n A l l ( t s ) } f u n c ( r * R u n C o u n t e r 2 ) C o u n t ( ) i n t { r e t u r n r . c o u n t }
48. Is struct embedding like inheritance? No, it is better! It is composition. You can't reach into another type and change the way it works. Method dispatching is explicit. It is more general. Struct embedding of interfaces.
49. Is struct embedding like inheritance? Struct embedding is selective. / / W r i t e C o u n t e r t r a c k s t h e t o t a l n u m b e r o f b y t e s w r i t t e n . t y p e W r i t e C o u n t e r s t r u c t { i o . R e a d W r i t e r c o u n t i n t } f u n c ( w * W r i t e C o u n t e r ) W r i t e ( b [ ] b y t e ) ( i n t , e r r o r ) { w . c o u n t + = l e n ( b ) r e t u r n w . R e a d W r i t e r . W r i t e ( b ) } WriteCounter can be used with any i o . R e a d W r i t e r . f u n c m a i n ( ) { b u f : = & b y t e s . B u f f e r { } w : = & W r i t e C o u n t e r { R e a d W r i t e r : b u f } f m t . F p r i n t f ( w , " H e l l o , g o p h e r s ! \ n " ) f m t . P r i n t f ( " P r i n t e d % v b y t e s " , w . c o u n t ) } Run
50. Easy mocking What if we wanted to fake a part of a n e t . C o n n ? t y p e C o n n i n t e r f a c e { R e a d ( b [ ] b y t e ) ( n i n t , e r r e r r o r ) W r i t e ( b [ ] b y t e ) ( n i n t , e r r e r r o r ) C l o s e ( ) e r r o r L o c a l A d d r ( ) A d d r R e m o t e A d d r ( ) A d d r S e t D e a d l i n e ( t t i m e . T i m e ) e r r o r S e t R e a d D e a d l i n e ( t t i m e . T i m e ) e r r o r S e t W r i t e D e a d l i n e ( t t i m e . T i m e ) e r r o r } I want to test h a n d l e C o n : f u n c h a n d l e C o n n ( c o n n n e t . C o n n ) { We could create a f a k e C o n n and define all the methods of C o n n on it. But that's a lot of boring code.
51. Struct embedding of interfaces WARNING : Cool stuff If a type T has an embedded field of a type E, all the methods of E will be defined on T. Therefore, if E is an interface T satisfies E.
52. Struct embedding of interfaces (continued) We can test h a n d l e C o n with the l o o p B a c k type. t y p e l o o p B a c k s t r u c t { n e t . C o n n b u f b y t e s . B u f f e r } Any calls to the methods of n e t . C o n n will fail, since the field is nil. We redefine the operations we support: f u n c ( c * l o o p B a c k ) R e a d ( b [ ] b y t e ) ( i n t , e r r o r ) { r e t u r n c . b u f . R e a d ( b ) } f u n c ( c * l o o p B a c k ) W r i t e ( b [ ] b y t e ) ( i n t , e r r o r ) { r e t u r n c . b u f . W r i t e ( b ) }
53. Concurrency
54. Concurrency It is part of the language, not a library. Based on two concepts: goroutines: lightweight threads channels: typed pipes used to communicate and synchronize between goroutines So cheap you can use them whenever you want.
55. Sleep and talk f u n c s l e e p A n d T a l k ( t t i m e . D u r a t i o n , m s g s t r i n g ) { t i m e . S l e e p ( t ) f m t . P r i n t f ( " % v " , m s g ) } We want a message per second. What if we started all the s l e e p A n d T a l k concurrently? Just add g o ! f u n c m a i n ( ) { s l e e p A n d T a l k ( 0 * t i m e . S e c o n d , " H e l l o " ) s l e e p A n d T a l k ( 1 * t i m e . S e c o n d , " G o p h e r s ! " ) s l e e p A n d T a l k ( 2 * t i m e . S e c o n d , " W h a t ' s " ) s l e e p A n d T a l k ( 3 * t i m e . S e c o n d , " u p ? " ) } Run
56. Concurrent sleep and talk That was fast ... When the m a i n goroutine ends, the program ends. f u n c m a i n ( ) { g o s l e e p A n d T a l k ( 0 * t i m e . S e c o n d , " H e l l o " ) g o s l e e p A n d T a l k ( 1 * t i m e . S e c o n d , " G o p h e r s ! " ) g o s l e e p A n d T a l k ( 2 * t i m e . S e c o n d , " W h a t ' s " ) g o s l e e p A n d T a l k ( 3 * t i m e . S e c o n d , " u p ? " ) } Run
57. Concurrent sleep and talk with more sleeping But synchronizing with S l e e p is a bad idea. f u n c m a i n ( ) { g o s l e e p A n d T a l k ( 0 * t i m e . S e c o n d , " H e l l o " ) g o s l e e p A n d T a l k ( 1 * t i m e . S e c o n d , " G o p h e r s ! " ) g o s l e e p A n d T a l k ( 2 * t i m e . S e c o n d , " W h a t ' s " ) g o s l e e p A n d T a l k ( 3 * t i m e . S e c o n d , " u p ? " ) t i m e . S l e e p ( 4 * t i m e . S e c o n d ) } Run
58. Communicating through channels s l e e p A n d T a l k sends the string into the channel instead of printing it. f u n c s l e e p A n d T a l k ( s e c s t i m e . D u r a t i o n , m s g s t r i n g , c c h a n s t r i n g ) { t i m e . S l e e p ( s e c s * t i m e . S e c o n d ) c < - m s g } We create the channel and pass it to s l e e p A n d T a l k , then wait for the values to be sent. f u n c m a i n ( ) { c : = m a k e ( c h a n s t r i n g ) g o s l e e p A n d T a l k ( 0 , " H e l l o " , c ) g o s l e e p A n d T a l k ( 1 , " G o p h e r s ! " , c ) g o s l e e p A n d T a l k ( 2 , " W h a t ' s " , c ) g o s l e e p A n d T a l k ( 3 , " u p ? " , c ) f o r i : = 0 ; i < 4 ; i + + { f m t . P r i n t f ( " % v " , < - c ) } } Run
59. Let's count on the web We receive the next id from a channel. v a r n e x t I D = m a k e ( c h a n i n t ) f u n c h a n d l e r ( w h t t p . R e s p o n s e W r i t e r , q * h t t p . R e q u e s t ) { f m t . F p r i n t f ( w , " < h 1 > Y o u g o t % v < h 1 > " , < - n e x t I D ) } We need a goroutine sending ids into the channel. localhost:8080/next (http://localhost:8080/next) f u n c m a i n ( ) { h t t p . H a n d l e F u n c ( " / n e x t " , h a n d l e r ) g o f u n c ( ) { f o r i : = 0 ; ; i + + { n e x t I D < - i } } ( ) h t t p . L i s t e n A n d S e r v e ( " l o c a l h o s t : 8 0 8 0 " , n i l ) } Run
60. Let's fight! s e l e c t allows us to chose among multiple channel operations. Go - localhost:8080/fight?usr=go (http://localhost:8080/fight?usr=go) Java - localhost:8080/fight?usr=java (http://localhost:8080/fight?usr=java) v a r b a t t l e = m a k e ( c h a n s t r i n g ) f u n c h a n d l e r ( w h t t p . R e s p o n s e W r i t e r , q * h t t p . R e q u e s t ) { s e l e c t { c a s e b a t t l e < - q . F o r m V a l u e ( " u s r " ) : f m t . F p r i n t f ( w , " Y o u w o n ! " ) c a s e w o n : = < - b a t t l e : f m t . F p r i n t f ( w , " Y o u l o s t , % v i s b e t t e r t h a n y o u " , w o n ) } } Run
61. Chain of gophers Ok, I'm just bragging here
62. Chain of gophers f u n c f ( l e f t , r i g h t c h a n i n t ) { l e f t < - 1 + < - r i g h t } f u n c m a i n ( ) { s t a r t : = t i m e . N o w ( ) c o n s t n = 1 0 0 0 l e f t m o s t : = m a k e ( c h a n i n t ) r i g h t : = l e f t m o s t l e f t : = l e f t m o s t f o r i : = 0 ; i < n ; i + + { r i g h t = m a k e ( c h a n i n t ) g o f ( l e f t , r i g h t ) l e f t = r i g h t } g o f u n c ( c c h a n i n t ) { c < - 0 } ( r i g h t ) f m t . P r i n t l n ( < - l e f t m o s t , t i m e . S i n c e ( s t a r t ) ) } Run
63. Concurrency is very powerful And there's lots to learn! Go Concurrency Patterns (http://talks.golang.org/2012/concurrency.slide#1) , by Rob Pike Advanced Concurrency Patterns (http://talks.golang.org/2013/advconc.slide#1) , by Sameer Ajmani Concurrency is not Parellelism (http://talks.golang.org/2012/waza.slide#1) , by Rob Pike
64. In conclusion Go is simple, consistent, readable, and fun. All types are equal methods on any type Implicit interfaces Structural typing Less dependencies Code testable and reusable Use composition instead of inheritance Struct embedding to remove boilerplate. Struct embedding of interfaces to satisfy them fast. Concurrency is awesome, and you should check it out.
65. What to do next? Learn Go on your browser with tour.golang.org (http://tour.golang.org) Find more about Go on golang.org (http://golang.org) Join the community at golang-nuts (https://groups.google.com/forum/#!forum/Golang-nuts) Link to the slides talks.golang.org/2014/go4java.slide (http://talks.golang.org/2014/go4java.slide)
66. Thank you Francesc Campoy Gopher and Developer Advocate Google @francesc (http://twitter.com/francesc) campoy@golang.org (mailto:campoy@golang.org)