Introduction to Go (golang) 04 Nov 2015 Niket Patel Director, Beehively 

What is Go? G o i s a n o p e n s o u r c e p r o g r a m m i n g l a n g u a g e t h a t m a k e s i t e a s y t o b u i l d s i m p l e , r e l i a b l e , a n d e f f i c i e n t s o f t w a r e . - h t t p : / / g o l a n g . o r g 

Hello, World p a c k a g e m a i n f u n c m a i n ( ) { p r i n t ( " H e l l o , अहमदाबाद . " ) } Run 

Features of Go Concurrency GC Interfaces Composition (over inheritance) Orthogonal Fast compilation Cross compilation Static Binary NO classical OOP 

Projects built using Go Docker dl.google.com (downloads from google) vitess.io (mysql proxy developed by youtube) CoreOS Google kubernetes InfluxDB https://github.com/golang/go/wiki/Projects 

Companies using Go Beehively Google Dropbox Heroku Github Twitter Canonical (Ubuntu) Cloudflare bit.ly ThoughtWorks Qwinix More... (https://github.com/golang/go/wiki/GoUsers) 

Introduction to Go Syntax 

Packages, Imports ValueOfPi function is exported and visible outside package. calculatedPi function is visible only inside package. p a c k a g e m a i n i m p o r t " f m t " i m p o r t " m a t h " c o n s t L i m i t = 1 0 0 0 0 0 0 0 0 v a r l i m i t = 1 0 0 0 0 0 0 0 0 f u n c m a i n ( ) { f m t . P r i n t l n ( " P I : \ n C a l c u l a t e d " , V a l u e O f P i ( ) , " \ n C o n s t a n t " , m a t h . P i ) } f u n c V a l u e O f P i ( ) f l o a t 6 4 { r e t u r n c a l c u l a t e d P i ( L i m i t ) } f u n c c a l c u l a t e d P i ( l i m i t f l o a t 6 4 ) f l o a t 6 4 { Run 

Variables f u n c c a l c u l a t e d P i ( l i m i t f l o a t 6 4 ) f l o a t 6 4 { v a r s u m f l o a t 6 4 v a r n u m , t o g g l e = 4 . 0 , t r u e f o r i : = 1 . 0 ; i < l i m i t ; i + = 2 { i f t o g g l e { s u m + = n u m / i } e l s e { s u m - = n u m / i } t o g g l e = ! t o g g l e } r e t u r n s u m } Run 

Conditions p a c k a g e m a i n i m p o r t " f m t " v a r a g e L i m i t = 6 0 f u n c m a i n ( ) { v a r a g e = 3 6 i f o v e r l i m i t ( a g e ) { f m t . P r i n t l n ( a g e , " i s o v e r l i m i t " ) } e l s e { f m t . P r i n t l n ( a g e , " i s u n d e r l i m i t " ) } } f u n c o v e r l i m i t ( a g e i n t ) b o o l { r e t u r n a g e > a g e L i m i t } Run 

Loops f u n c m a i n ( ) { v a r l o o p b o o l v a r i t e m s = [ ] s t r i n g { " O n e " , " T w o " , " T h r e e " } f o r i , i t e m : = r a n g e i t e m s { f m t . P r i n t l n ( i , i t e m ) } f o r i : = 0 ; i < l e n ( i t e m s ) ; i + + { f m t . P r i n t l n ( i , i t e m s [ i ] ) } f o r l o o p { f m t . P r i n t l n ( " N e v e r r e a c h e d " ) } f o r { / / i n f i n i t e l o o p } } Run 

Functions f u n c m a i n ( ) { f m t . P r i n t l n ( g e t A g e ( ) ) f m t . P r i n t l n ( g e t N a m e A n d A g e ( ) ) f m t . P r i n t l n ( b e t t e r N a m e A n d A g e ( ) ) } f u n c g e t A g e ( ) i n t { r e t u r n 3 3 } f u n c g e t N a m e A n d A g e ( ) ( n a m e s t r i n g , a g e i n t ) { n a m e = " J o h n " a g e = g e t A g e ( ) r e t u r n } f u n c b e t t e r N a m e A n d A g e ( ) ( s t r i n g , i n t ) { n a m e : = " J o h n " r e t u r n n a m e , g e t A g e ( ) } Run 

Structs t y p e A g e s t r u c t { t i m e . D u r a t i o n } t y p e P e r s o n s t r u c t { f i r s t N a m e , l a s t N a m e s t r i n g o c c u p a t i o n s t r i n g a g e A g e } f u n c m a i n ( ) { p e r s o n : = P e r s o n { } p e r s o n . f i r s t N a m e = " V i j a y " p e r s o n . l a s t N a m e = " D e e n a n a t h C h a u h a n " p e r s o n . a g e = A g e { 3 6 * 3 6 5 * 2 4 * t i m e . H o u r } f m t . P r i n t l n ( p e r s o n . f i r s t N a m e , p e r s o n . l a s t N a m e , " i s " , p e r s o n . a g e , " o l d . " ) } Run 

Methods f u n c ( t P e r s o n ) S a y N a m e ( ) s t r i n g { r e t u r n f m t . S p r i n t f ( " M y N a m e i s % s \ n . . . % s % s " , t . l a s t N a m e , t . f i r s t N a m e , t . l a s t N a m e , ) } f u n c m a i n ( ) { p e r s o n : = P e r s o n { } p e r s o n . f i r s t N a m e = " J a m e s " p e r s o n . l a s t N a m e = " B o n d " f m t . P r i n t l n ( p e r s o n . S a y N a m e ( ) ) } Run 

Methods f u n c ( t A g e n t ) S t r i n g ( ) s t r i n g { r e t u r n f m t . S p r i n t f ( " M y N a m e i s % s \ n . . . % s % s " , t . l a s t N a m e , t . f i r s t N a m e , t . l a s t N a m e , ) } f u n c m a i n ( ) { a g e n t : = A g e n t { } a g e n t . f i r s t N a m e = " J a m e s " a g e n t . l a s t N a m e = " B o n d " f m t . P r i n t l n ( a g e n t ) } Run 

Zero Value p a c k a g e m a i n i m p o r t " f m t " t y p e A s t r u c t { n a m e s t r i n g a g e f l o a t 6 4 } f u n c m a i n ( ) { v a r s t r s t r i n g v a r n u m i n t 6 4 v a r a A f m t . P r i n t f ( " % # v , \ n % # v , \ n % # v \ n " , s t r , n u m , a ) } Run 

Interfaces t y p e M a s s i n t t y p e W o o d s t r u c t { M a s s } t y p e P a p e r s t r u c t { M a s s } t y p e B u r n e r i n t e r f a c e { C a n B u r n ( ) b o o l B u r n T i m e ( ) M a s s } 

Interfaces (cont'd...) f u n c ( m M a s s ) C a n B u r n ( ) b o o l { r e t u r n m > 0 } f u n c ( w W o o d ) B u r n T i m e ( ) M a s s { r e t u r n 1 0 * w . M a s s } f u n c ( p P a p e r ) B u r n T i m e ( ) M a s s { r e t u r n 1 * p . M a s s } f u n c B u r n ( b B u r n e r ) { i f b . C a n B u r n ( ) { f m t . P r i n t f ( " % T w i l l b u r n f o r % d s e c o n d s \ n " , b , b . B u r n T i m e ( ) ) } e l s e { f m t . P r i n t f ( " % T c a n ' t b u r n \ n " , b ) } } f u n c m a i n ( ) { B u r n ( W o o d { 1 0 } ) B u r n ( P a p e r { 1 0 } ) B u r n ( P a p e r { 0 } ) } / / Run 

Pointers p a c k a g e m a i n i m p o r t " f m t " f u n c m a i n ( ) { v a r a i n t a = 3 f m t . P r i n t l n ( a , & a ) f m t . P r i n t f ( " % T % T \ n " , a , & a ) v a r b i n t v a r p * i n t f m t . P r i n t l n ( b , p ) p = & b f m t . P r i n t l n ( b , p ) } Run 

Pointers (cont'd...) p a c k a g e m a i n i m p o r t " f m t " 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 m a i n ( ) { a : = P e r s o n { " A " } f m t . P r i n t l n ( a . n a m e ) a . c h a n g e N a m e ( ) f m t . P r i n t ( a . n a m e ) } f u n c ( p P e r s o n ) c h a n g e N a m e ( ) { p . n a m e = " B " } Run 

Slices p a c k a g e m a i n i m p o r t " f m t " f u n c m a i n ( ) { v a r a [ ] s t r i n g a = a p p e n d ( a , " V i j a y " ) f m t . P r i n t l n ( a ) v a r b = [ ] s t r i n g { " 1 " , " 2 " , " 3 " , " 4 " , " 5 " } f m t . P r i n t l n ( b ) } Run 

Slices p a c k a g e m a i n i m p o r t " f m t " f u n c m a i n ( ) { v a r a = [ 3 ] s t r i n g { " 1 " , " V i j a y " , " 3 " } v a r b = a [ 0 : 3 ] / / c r e a t e s l i c e f r o m a r r a y f m t . P r i n t l n ( b ) b = a p p e n d ( b , " 4 " ) b = a p p e n d ( b , " 5 " ) f m t . P r i n t l n ( b ) } Run 

Maps p a c k a g e m a i n i m p o r t " f m t " f u n c m a i n ( ) { v a r m m a p [ s t r i n g ] f l o a t 6 4 m [ " v a l u e O f Z e r o " ] = 0 . 0 f m t . P r i n t l n ( m [ " v a l u e O f Z e r o " ] ) } Run 

Maps p a c k a g e m a i n i m p o r t " f m t " t y p e W e e k d a y i n t v a r d a y s = m a k e ( m a p [ i n t ] s t r i n g ) f u n c i n i t ( ) { d a y s [ 0 ] = " S u n d a y " d a y s [ 1 ] = " M o n d a y " d a y s [ 2 ] = " T u e s d a y " } f u n c m a i n ( ) { v a r d W e e k d a y f m t . P r i n t l n ( d ) } f u n c ( d W e e k d a y ) S t r i n g ( ) s t r i n g { r e t u r n d a y s [ i n t ( d ) ] } Run 

Error handling p a c k a g e m a i n i m p o r t ( " i o " " o s " ) f u n c m a i n ( ) { f i l e , e r r : = o s . O p e n ( " e r r 2 . g o " ) d i e ( e r r ) i o . C o p y ( o s . S t d o u t , f i l e ) } f u n c d i e ( e r r e r r o r ) { i f e r r ! = n i l { p a n i c ( e r r ) } } Run 

Error handling (Cont'd...) p a c k a g e m a i n i m p o r t ( " i o " " l o g " " o s " ) f u n c m a i n ( ) { f i l e , e r r : = o s . O p e n ( " e r r . g o " ) i f e r r ! = n i l { l o g . P r i n t l n ( e r r ) } i f _ , e r r : = i o . C o p y ( o s . S t d o u t , f i l e ) ; e r r ! = n i l { l o g . P r i n t l n ( e r r ) } } Run 

Embedding t y p e R e a d e r i n t e r f a c e { R e a d ( p [ ] b y t e ) ( n i n t , e r r e r r o r ) } t y p e W r i t e r i n t e r f a c e { W r i t e ( p [ ] b y t e ) ( n i n t , e r r e r r o r ) } t y p e R e a d e r W r i t e r i n t e r f a c e { R e a d e r W r i t e r } 

Embedding (cont'd...) t y p e P e r s o n s t r u c t { f i r s t N a m e , l a s t N a m e s t r i n g } t y p e T e a c h e r s t r u c t { P e r s o n S u b j e c t s t r i n g } f u n c m a i n ( ) { t : = T e a c h e r { } t . f i r s t N a m e = " J o h n " t . l a s t N a m e = " D o e " t . S u b j e c t = " E n g l i s h " f m t . P r i n t l n ( t ) } f u n c ( t T e a c h e r ) S t r i n g ( ) s t r i n g { r e t u r n f m t . S p r i n t f ( " % s % s ( % s ) " , t . f i r s t N a m e , t . l a s t N a m e , t . S u b j e c t ) } Run 

Concurrency 

Concurrency is not Parallelism Concurrency is when two tasks can start, run, and complete in overlapping time periods. It doesn't necessarily mean they'll ever both be running at the same instant. Parallelism is when tasks literally run at the same time. 

Concurrency Primitives in Go Goroutines ("go" keyword) select channel types channel operators 

Concurrency Primitives in Go f u n c m a i n ( ) { f o r n u m : = 0 ; n u m < 2 0 ; n u m + + { j o b ( n u m ) } } f u n c j o b ( n u m i n t ) { t i m e . S l e e p ( t i m e . D u r a t i o n ( n u m * 1 2 0 ) * t i m e . M i l l i s e c o n d ) f m t . P r i n t l n ( " J o b " , n u m ) } Run 

Concurrency Primitives in Go f u n c m a i n ( ) { f o r n u m : = 0 ; n u m < 2 0 ; n u m + + { g o j o b ( n u m ) } t i m e . S l e e p ( 5 * t i m e . S e c o n d ) } f u n c j o b ( n u m i n t ) { t i m e . S l e e p ( t i m e . D u r a t i o n ( n u m * 1 2 0 ) * t i m e . M i l l i s e c o n d ) f m t . P r i n t l n ( " J o b " , n u m ) } Run 

Concurrency Primitives in Go f u n c m a i n ( ) { v a r w g s y n c . W a i t G r o u p f o r n u m : = 0 ; n u m < 2 0 ; n u m + + { w g . A d d ( 1 ) g o j o b ( n u m , & w g ) } w g . W a i t ( ) } f u n c j o b ( n u m i n t , w g * s y n c . W a i t G r o u p ) { t i m e . S l e e p ( t i m e . D u r a t i o n ( n u m * 1 2 0 ) * t i m e . M i l l i s e c o n d ) f m t . P r i n t l n ( " J o b " , n u m ) w g . D o n e ( ) } Run 

Concurrency Primitives in Go f u n c m a i n ( ) { c o u n t , t 1 : = 1 0 , t i m e . N o w ( ) v a r r e s u l t = m a k e ( c h a n i n t ) f o r i : = 0 ; i < c o u n t ; i + + { g o j o b ( r e s u l t ) } f o r i : = 0 ; i < c o u n t ; i + + { f m t . P r i n t l n ( " J o b " , i , " " , < - r e s u l t ) } f m t . P r i n t l n ( " T o o k " , t i m e . N o w ( ) . S u b ( t 1 ) ) } f u n c j o b ( r e s u l t c h a n i n t ) { r e s u l t < - d o J o b ( ) } Run 

Concurrency Primitives in Go f u n c m a i n ( ) { c o u n t , t 1 : = 1 0 , t i m e . N o w ( ) d e f e r f u n c ( ) { f m t . P r i n t l n ( " T o o k " , t i m e . N o w ( ) . S u b ( t 1 ) ) } ( ) v a r r e s u l t = m a k e ( c h a n i n t ) f o r i : = 0 ; i < c o u n t ; i + + { g o j o b ( r e s u l t ) } t i m e o u t : = t i m e . N e w T i m e r ( 2 * t i m e . S e c o n d ) f o r i : = 0 ; i < c o u n t ; i + + { s e l e c t { c a s e r e s : = < - r e s u l t : f m t . P r i n t l n ( " J o b " , i , " " , r e s ) c a s e < - t i m e o u t . C : r e t u r n } } } Run 

Resources How to write Go code (https://www.youtube.com/watch?v=XCsL89YtqCs) How I start (https://howistart.org/posts/go/1) Go Tour (https://tour.golang.org/welcome/1) Effective Go (https://golang.org/doc/effective_go.html) 

Thank you 04 Nov 2015 Tags: meetup, golang, introduction (#ZgotmplZ) Niket Patel Director, Beehively [email protected] (mailto:[email protected]) @nexneo (http://twitter.com/nexneo) 

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