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course/13-channels/exercises/5-close/readme.md

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+# Closing channels in Go
+
+Channels can be explicitly closed by a *sender*:
+
+```go
+ch := make(chan int)
+
+// do some stuff with the channel
+
+close(ch)
+```
+
+## Checking if a channel is closed
+
+Similar to the `ok` value when accessing data in a `map`, receivers can check the `ok` value when receiving from a channel to test if a channel was closed.
+
+```go
+v, ok := <-ch
+```
+
+ok is `false` if the channel is empty and closed.
+
+## Don't send on a closed channel
+
+Sending on a closed channel will cause a panic. A panic on the main goroutine will cause the entire program to crash, and a panic in any other goroutine will cause *that goroutine* to crash.
+
+Closing isn't necessary. There's nothing wrong with leaving channels open, they'll still be garbage collected if they're unused. You should close channels to indicate explicitly to a receiver that nothing else is going to come across.
+
+## Assignment
+
+At Mailio we're all about keeping track of what our systems are up to with great logging and [telemetry](https://en.wikipedia.org/wiki/Telemetry).
+
+The `sendReports` function sends out a batch of reports to our clients and reports back how many were sent across a channel. It closes the channel when it's done.
+
+Complete the `countReports` function. It should:
+
+* Use an infinite `for` loop to read from the channel:
+* If the channel is closed, break out of the loop
+* Otherwise, keep a running total of the number of reports sent
+* Return the total number of reports sent