What is the advantage of sending to a channel using select in Go?

Question

The example Gorilla websocket directory contains the hub.go file.

https://github.com/gorilla/websocket/blob/master/examples/chat/hub.go

Here you can find a method in a type hub that does this.

func (h *hub) run() {
    for {
        select {
        case c := <-h.register:
            h.connections[c] = true
        case c := <-h.unregister:
            if _, ok := h.connections[c]; ok {
                delete(h.connections, c)
                close(c.send)
            }
        case m := <-h.broadcast:
            for c := range h.connections {
                select {
                case c.send <- m:
                default:
                    close(c.send)
                    delete(h.connections, c)
                }
            }
        }
    }
}

Why doesn't he just send the c.send channel directly in the latter case?

case m := <-h.broadcast:
    for c := range h.connections {
        c.send <- m
    }

Answer 1

This guaranteed non-blocking method is sent to the channel. In case c.send chan cannot accept new messages now, the default branch will be executed. Without select {}, sending a block to an unbuffered or full buffer channel may be blocked.

Answer 2

https://gobyexample.com/non-blocking-channel-operations

// Basic sends and receives on channels are blocking.
// However, we can use `select` with a `default` clause to
// implement _non-blocking_ sends, receives, and even
// non-blocking multi-way `select`s.

package main

import "fmt"

func main() {
    messages := make(chan string)
    //[...]

    // Here a non-blocking receive. If a value is
    // available on `messages` then `select` will take
    // the `<-messages` `case` with that value. If not
    // it will immediately take the `default` case.
    select {
    case msg := <-messages:
        fmt.Println("received message", msg)
    default:
        fmt.Println("no message received")
    }

    // A non-blocking send works similarly.
    msg := "hi"
    select {
    case messages <- msg:
        fmt.Println("sent message", msg)
    default:
        fmt.Println("no message sent")
    }
    //[...]
}

: "" case , , . default