delete map[key] in go?

Question

i have a map:

var sessions = map[string] chan int{}

How do i delete sessions[key] ?

tried:

sessions[key] = nil,false;

That did'nt work.

Answer 1

From Effective Go:

To delete a map entry, turn the multiple assignment around by placing an extra boolean on the right; if the boolean is false, the entry is deleted. It's safe to do this even if the key is already absent from the map.

timeZone["PDT"] = 0, false;  // Now on Standard Time

Answer 2

Use make (chan int) instead of nil. The first value has to be the same type that your map holds.

package main

import "fmt"

func main() {

    var sessions = map[string] chan int{};
    sessions["somekey"] = make(chan int);

    fmt.Printf ("%d\n", len(sessions)); // 1

    // Remove somekey's value from sessions
    sessions["somekey"] = make(chan int), false;

    fmt.Printf ("%d\n", len(sessions)); // 0
}

UPDATE: Corrected my answer.

Answer 3

Strangely enough,

package main

func main () {
    var sessions = map[string] chan int{};
    sessions["moo"] = make (chan int), false;
}

seems to work. This seems a poor use of resources though!

Another way is to check for existence and use the value itself:

package main

func main () {
    var sessions = map[string] chan int{};
    sessions["moo"] = make (chan int);
    _, ok := sessions["moo"];
    if ok {
        sessions["moo"] = sessions["moo"], false;
    }
}