Going Async in Go

defer.go

package main

import (
    "bufio"
    "fmt"
    "os"
)

func main() {
    syslog, err := os.Open("/var/log/system.log")
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        os.Exit(1)
    }
    defer syslog.Close() // called after the for loop
    
    scanner := bufio.NewScanner(syslog)
    for scanner.Scan() {
        fmt.Println(scanner.Text())
    }
}

forwarders.go

package main

import "fmt"

func increased(source <-chan int) chan int {
    increased := make(chan int)
    go func() {
        for {
            increased <- (<-source + 1)
        }
    }()
    return increased
}

func main() {
    first := make(chan int)
    var result = first
    for i := 1; i <= 100000; i++ {
        result = increased(result)
    }

    first <- 1
    fmt.Printf("Result is %d", <-result)
}

hello-world.go

package main

import "fmt"

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

maps.go

package main

func main() {
    // make a map
    ages := make(map[string]int)
    ages["John"] = 83
    ages["Jane"] = 23
    
    // now with a literal
    phoneNumbers := map[string]string{"John": "555-GO-ROCKS", "Jane": "555-MAPS-TOO"}
    
    // delete John's number
    delete(phoneNumbers, "John")
}

non-blocking.go

package main

import (
    "fmt"
    "net/http"
    "sync"
)

func get(url string, wg *sync.WaitGroup) {
    defer wg.Done()
    if _, err := http.Get(url); err != nil {
        fmt.Println("Failed to get", url, err)
    } else {
        fmt.Println("Got", url)
    }
}

func main() {
    urls := []string{"http://google.com", "http://bing.com", "http://yahoo.com"}
    var wg sync.WaitGroup

    for _, url := range urls {
        wg.Add(1)
        go get(url, &wg) // pass a pointer to wg
    }
    wg.Wait()
    fmt.Println("All done!")
}

slices.go

package main

func main() {
    // a slices with an initial length of 2
    persons := make([]string, 2)
    persons[0] = "John"
    persons[1] = "Jane"
    
    // a slice can be declared and initialized with a literal
    ages := []int{15,23,49,84}
    
    // get sub-sequences using the slice operator
    exceptFirstTwo := ages[2:] // including ages[2]
    justFirstTwo := ages[:2] // not including ages[2]
}

timing-out.go

package main

import (
    "fmt"
    "net/http"
    "time"
)

func get(url string) chan string {
    result := make(chan string)
    go func() {
        _, err := http.Get(url)
        if err != nil {
            result <- "Failed"
        } else {
            result <- "Success"
        }
    }()
    return result
}

func main() {
    select {
    case result := <-get("http://whatever.herokuapp.com"):
        fmt.Println(result)
    case <- time.After(time.Millisecond * 500):
        fmt.Println("That server is too god damn slow")
    }
}

variables.go

package main

func modify(names *[2]string) {
    names[0] = "John Travolta"
}

func main() {
    // a variable declared and initialized with explicit type
    var firstName string = "John"
    
    // using shorthand syntax and type inference
    lastName := "Doe"
    
    // a constant value
    const weather = "rain"
    
    names := [2]string{"Jackie Chan", "Mark Wahlberg"}
    // passing pointers to variables
    modify(&names)
}