package main
import (
"fmt"
)
var store = map[string]int{}
func breadArrived(num int) {
if breadTotal, ok := store["bread"]; ok {
breadTotal += num
} else {
store["bread"] = num
}
fmt.Printf("%v
", store)
}
func main() {
breadArrived(1)
breadArrived(2)
breadArrived(3)
}
Code above ignores the += operator, so store["bread"] always equals to 1. I assume I'm missing something like "passing by reference" here. Also, is there any more convenient way of doing this?
Thanks.
You're only incrementing the breadTotal local variable, and not the value in the store map. It should be:
store["bread"] = breadTotal + num
Also you can simply do:
store["bread"] += num
Also since indexing a map returns the zero value of the value type for keys which are not yet in the map (zero value for int is 0 – properly telling no bread yet), that if is completely unnecessary. You can simply do:
func breadArrived(num int) {
store["bread"] += num
fmt.Printf("%v
", store)
}
Output (try it on the Go Playground):
map[bread:1]
map[bread:3]
map[bread:6]
The breadTotal variable is only a copy of the map integer value, you need to reference it as store["bread"] += num to increment the map integer value.
https://play.golang.org/p/LQzrbSZudH
package main
import (
"fmt"
)
var store = map[string]int{}
func breadArrived(num int) {
store["bread"] += num
fmt.Printf("%v
", store)
}
func main() {
breadArrived(1)
breadArrived(2)
breadArrived(3)
}
By the way, the first incrementing of the map integer works because go initializes everything to a default value, in the case of integers the default value is 0.
Simple increment like C\C++ style:
package main
import (
"fmt"
)
var store = map[string]int{}
func main() {
store["some_key"] = 0
if _, found:= store["some_key"]; found{
fmt.Println(store["some_key"])
store["some_key"]++
fmt.Println(store["some_key"])
}
}