// Created on savesnippets.com · https://savesnippets.com/q9NF5fyNe94FcU
package main

import (
    "fmt"
    "sync"
    "time"
)

func main() {
    var wg sync.WaitGroup
    urls := []string{"a", "b", "c", "d"}

    for _, u := range urls {
        wg.Add(1)                              // increment BEFORE go
        go func(url string) {
            defer wg.Done()                    // decrement when goroutine exits
            time.Sleep(100 * time.Millisecond)
            fmt.Println("fetched", url)
        }(u)                                   // pass `u` as arg — avoid closure capture bug
    }

    wg.Wait()                                  // blocks until all Done() called
    fmt.Println("all done")
}