typesP.go

package main

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"os"
)

// user-defined type based on struct built-in type
type webPage struct {
	url  string
	body []byte
	err  error
}

// webPage's method
func (w *webPage) get() {
	resp, err := http.Get(w.url)
	if err != nil {
		w.err = err
		return
	}
	defer resp.Body.Close()

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		w.err = err
	}
	w.body = body
}

// wrapper around get() to allow parallelism
func getp(w *webPage, ch chan<- string) {
	w.get()
	ch <- fmt.Sprintf("url: %s, len: %d, err: %v", w.url, len(w.body), w.err)
}

func main() {
	if !(len(os.Args) > 1) {
		fmt.Fprintf(os.Stderr, "Usage: typesS url [url ...]\n")
		os.Exit(1)
	}

	// create a channel -- communication mechanism that allows one goroutine to
	// pass values of a specified type to another goroutine
	ch := make(chan string)

	// get all urls in parallel
	for _, url := range os.Args[1:] {
		w := &webPage{url: url}
		go getp(w, ch)
	}

	// print results in parallel
	for range os.Args[1:] {
		fmt.Println(<-ch)
	}
}