Goroutine to populate struct instance slice

Question

This is my first day using Go and I had a question about goroutines and appending to an instance's slice.

The idea is that each Truck would have a Cargo of length 1 containing an Item with name "Groceries". I almost have it, but for some reason it's losing the properties of the truck, and it seems to be terminating prematurely.

https://play.golang.org/p/f0uIy5qg8d

 package main import "fmt" import "time" type Item struct { name string } type Truck struct{ Cargo []Item name string } func UnloadTrucks(ch chan *Truck){ t := <- ch fmt.Printf("%s has %d items in cargo: %s\\n", t.name, len(t.Cargo), t.Cargo[0].name) time.Sleep(1 * time.Second) return } func main() { trucks := make([]Truck, 2) ch := make(chan *Truck) for i, t := range trucks{ t.name = fmt.Sprintf("Truck %d", i + 1) fmt.Printf("Building %s\\n", t.name) } for _, t := range trucks { go func(tr *Truck){ itm := Item {} itm.name = "Groceries" fmt.Printf("Loading %s", tr.name) tr.Cargo = append(tr.Cargo, itm) ch <- tr }(&t) } UnloadTrucks(ch) } 

Answer 1

Your issue is not that the truck's properties are "lost", but they're never set in the first place. This loop is your problem:

for i, t := range trucks {
    t.name = fmt.Sprintf("Truck %d", i + 1)
    fmt.Printf("Building %s\n", t.name)
}

Within this loop, t is a copy of the Truck object in the trucks slice. Any modification on this object will not affect the original truck. Instead, you can reference the original Truck object by using the index variable i to directly access the object in the trucks slice:

for i, _ := range trucks {
    trucks[i].name = fmt.Sprintf("Truck %d", i + 1)
    fmt.Printf("Building %s\n", trucks[i].name)
}