Delete map[key] in go?

I have a map:

var sessions =  map[string] chan int{}

How do I delete sessions[key] ? I tried:

sessions[key] = nil,false;

That didn’t work.

Update (November 2011):

The special syntax for deleting map entries is removed in Go version 1:

Go 1 will remove the special map assignment and introduce a new built-in function, delete : delete(m, x) will delete the map entry retrieved by the expression m[x] . …

Strangely enough,

package main

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

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 {
        delete(sessions, "moo");
    }
}