LET'S GO-LANG

Luka Zakrajšek

CTO @ Koofr

@bancek

First Ljubljana Go Meetup

December 8, 2014

WHAT IS GOnew programming language from Googlelow levelC-like syntaxfast compilation (for large codebases)compiles to single librarycross platform (Windows, Linux, Mac)

WHAT IS GOstatically-typedmanaged memory (garbage collection)type safetydynamic-typing capabilitiesbuilt-in types (variable-length arrays and key-value maps)large standard library

GO IS C#include <stdio.h> main(){ printf("Hello World\n"); return 0;}

package main

import "fmt"

func main() { fmt.Println("Hello World")}

GO IS PYTHONimport reimport osimport Imageimport csvimport jsonimport gzipimport urllibimport unittest

import ( "regexp" "os.exec" "image/jpeg" "encoding/csv" "encoding/json" "compress/gzip" "net/http" "testing")

import "github.com/koofr/go-koofrclient"

GO IS NODE.JSvar http = require('http');http.createServer(function (req, res) { res.writeHead(200); res.end('Hello World');}).listen(1337, '127.0.0.1');console.log('Server running at http://127.0.0.1:1337/');

package mainimport ( "fmt" "net/http")func main() { http.HandleFunc("/", func (w http.ResponseWriter, r *http.Request) { fmt.Fprintf(w, "Hello World") }) http.ListenAndServe(":1337", nil) fmt.Println("Server running at http://127.0.0.1:1337/");}

BASIC CONSTRUCTS

PACKAGESlibraries structured in packagesprograms start running in package main

IMPORTSlocal imports (GOPATH env. variable)import directly from web (http, git, mercurial)capitalized identifiers are exported

import ( "fmt" "github.com/koofr/go-koofrclient")

FUNCTIONStake zero or more argumentsa function can return any number of results.types come after variable namesnamed return values

func myfunction(x, y int) (x int, y int) { tmp := x x = y y = tmp return // return y, x}

VARIABLESvar statement declares a list of variablestype comes after name

var c, python, java bool

func main() { var i int fmt.Println(i, c, python, java)}

short variable declarations

func main() { var i int = 1 k := 3 // type inference}

BASIC TYPESboolstringint, uint, int8, uint, int16, uint16, int32, uint32, int64, uint64,uintptrbyte // alias for uint8rune // alias for int32, represents a Unicode code pointfloat32, float64complex64, complex128

OTHER CONSTRUCTSpointersstructsarraysslicesmaps

INTERFACEStype Reader interface { Read(p []byte) (n int, err error)}

INTERFACEStype SizeReader struct { r io.Reader size int64}func (sr *SizeReader) Read(p []byte) (n int, err error) { n, err = sr.r.Read(p) sr.size += int64(n) return}func consumeReader(r io.Reader) { // ...}func main() { var sr *SizeReader = &SizeReader{myFile, 0} consumeReader(sr) fmt.Println(sr.size)}

GOROUTINES AND CHANNELSfunc doSomethingExpensive() int { time.Sleep(10 * time.Second) return 42}

func doItAsync() { go doSomethingExpensive()}

func doItAsyncAndGetResult() <-chan int { ch := make(chan int, 1) go func() { ch <- doSomethingExpensive() }() return ch}

ERROR HANDLINGfunc copyFile(src string, dest string) (i64, error) { r, err := os.Open(src) if err != nil { return err } defer r.Close()

w, err := os.Create(dest) if err != nil { return err } defer w.Close()

bytesCopied, err = io.Copy(w, r)

return bytesCopied, err}

GO COMMAND// fetch dependenciesgo get

// run testsgo test

// build binarygo build

// format codego fmt

// check for errors in codego vet

CODE STRUCTURE

LIBRARY STRUCTURE.gitignoreLICENSEREADME.mdcache.gocache_test.go

APPLICATION STRUCTUREsrc/ github.com/ koofr/ go-ioutils myapp/ internallib/ lib.go main/ main.go config.go myapp.go

bin/ myapppkg/build/dist/

TESTINGpackage newmath

import "testing"

func TestSqrt(t *testing.T) { const in, out = 4, 2 if x := Sqrt(in); x != out { t.Errorf("Sqrt(%v) = %v, want %v", in, x, out) }}

$ go testok github.com/user/newmath 0.165s

DEPLOYMENTgo build -o bin/myapp src/myapp/main/main.go

scp bin/myapp myserver.com:myapp

ssh myserver.com 'supervisorctl restart myapp'

GO @ KOOFRbackend

content server (downloads, uploads, streaming ...)FTP server...

desktop applicationGUI applicationsyncnative places

QUESTIONS?