Let's Go-lang

LET'S GO-LANG
Luka Zakrajšek
CTO @ Koofr
@bancek
First Ljubljana Go Meetup
December 8, 2014

WHAT IS GO
new programming language from Google
low level
C-like syntax
fast compilation (for large codebases)
compiles to single library
cross platform (Windows, Linux, Mac)

WHAT IS GO
statically-typed
managed memory (garbage collection)
type safety
dynamic-typing capabilities
built-in types (variable-length arrays and key-value maps)
large standard library

GO IS C
#include <stdio.h>
main()
{
printf("Hello Worldn");
return 0;
}
package main
import "fmt"
func main() {
fmt.Println("Hello World")
}

GO IS PYTHON
import re
import os
import Image
import csv
import json
import gzip
import urllib
import 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.JS
var 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 main
import (
"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/");
}

PACKAGES
libraries structured in packages
programs start running in package main

IMPORTS
local imports (GOPATH env. variable)
import directly from web (http, git, mercurial)
capitalized identifiers are exported
import (
"fmt"
"github.com/koofr/go-koofrclient"
)

FUNCTIONS
take zero or more arguments
a function can return any number of results.
types come after variable names
named return values
func myfunction(x, y int) (x int, y int) {
tmp := x
x = y
y = tmp
return
// return y, x
}

VARIABLES
var statement declares a list of variables
type 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 TYPES
bool
string
int, uint, int8, uint, int16, uint16, int32, uint32, int64, uint64,
uintptr
byte // alias for uint8
rune // alias for int32, represents a Unicode code point
float32, float64
complex64, complex128

OTHER CONSTRUCTS
pointers
structs
arrays
slices
maps

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

INTERFACES
type 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 CHANNELS
func 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 HANDLING
func 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 dependencies
go get
// run tests
go test
// build binary
go build
// format code
go fmt
// check for errors in code
go vet

LIBRARY STRUCTURE
.gitignore
LICENSE
README.md
cache.go
cache_test.go

APPLICATION STRUCTURE
src/
github.com/
koofr/
go-ioutils
myapp/
internallib/
lib.go
main/
main.go
config.go
myapp.go
bin/
myapp
pkg/
build/
dist/

TESTING
package 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 test
ok github.com/user/newmath 0.165s

DEPLOYMENT
go build -o bin/myapp src/myapp/main/main.go
scp bin/myapp myserver.com:myapp
ssh myserver.com 'supervisorctl restart myapp'

GO @ KOOFR
backend
content server (downloads, uploads, streaming ...)
FTP server
...
desktop application
GUI application
sync
native places

Let's Go-lang

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