select: change to empty struct and close (quii#276)

select.md

@@ -212,27 +212,30 @@ func Racer(a, b string) (winner string) {
     }
 }
 
-func ping(url string) chan bool {
-    ch := make(chan bool)
+func ping(url string) chan struct{} {
+    ch := make(chan struct{})
     go func() {
         http.Get(url)
-        ch <- true
+        close(ch)
     }()
     return ch
 }
 ```
 
 #### `ping`
 
-We have defined a function `ping` which creates a `chan bool` and returns it. 
+We have defined a function `ping` which creates a `chan struct{}` and returns it. 
 
-In our case, we don't really _care_ what the type sent in the channel, _we just want to send a signal_ to say we're finished so booleans are fine.
+In our case, we don't _care_ what type is sent to the channel, _we just want to signal we are done_ and closing the channel works perfectly!
+
+Why `struct{}` and not another type like a `bool`? Well, a `chan struct{}` is the smallest data type available from a memory perspective so we
+get no allocation versus a `bool`. Since we are closing and not sending anything on the chan, why allocate anything?
 
 Inside the same function, we start a goroutine which will send a signal into that channel once we have completed `http.Get(url)`.
 
 ##### Always `make` channels
 
-Notice how we have to use `make` when creating a channel; rather than say `var ch chan bool`. When you use `var` the variable will be initialised with the "zero" value of the type. So for `string` it is `""`, `int` it is 0, etc.
+Notice how we have to use `make` when creating a channel; rather than say `var ch chan struct{}`. When you use `var` the variable will be initialised with the "zero" value of the type. So for `string` it is `""`, `int` it is 0, etc.
 
 For channels the zero value is `nil` and if you try and send to it with `<-` it will block forever because you cannot send to `nil` channels
 

select/v2/racer.go

@@ -14,8 +14,8 @@ func Racer(a, b string) (winner string) {
 	}
 }
 
-func ping(url string) chan bool {
-	ch := make(chan bool)
+func ping(url string) chan struct{} {
+	ch := make(chan struct{})
 	go func() {
 		http.Get(url)
 		close(ch)

select/v3/racer.go

@@ -25,8 +25,8 @@ func ConfigurableRacer(a, b string, timeout time.Duration) (winner string, error
 	}
 }
 
-func ping(url string) chan bool {
-	ch := make(chan bool)
+func ping(url string) chan struct{} {
+	ch := make(chan struct{})
 	go func() {
 		http.Get(url)
 		close(ch)