concurrency

Sends values 0 through 9 into "in" channel and makes sure that they all come out in the correct order from the "out" channel.

Example and implementation are from: https://medium.com/capital-one-tech/building-an-unbounded-channel-in-go-789e175cd2cd.

in, out := InOut()
lastVal := -1
var wg sync.WaitGroup
wg.Add(1)

go func() {
	for v := range out {
		vi := v.(int)
		fmt.Println("Reading:", vi)
		if lastVal+1 != vi {
			panic("sequence is out of order")
		}
		lastVal = vi
	}
	wg.Done()
	fmt.Println("Finished reading!")
}()

for i := 0; i < 10; i++ {
	fmt.Println("Writing:", i)
	in <- i
}

close(in)
fmt.Println("Finished writing!")
wg.Wait()

if lastVal != 9 {
	panic("last value isn't 99")
}

Output:
Writing: 0
Writing: 1
Writing: 2
Writing: 3
Writing: 4
Writing: 5
Writing: 6
Writing: 7
Writing: 8
Writing: 9
Finished writing!
Reading: 0
Reading: 1
Reading: 2
Reading: 3
Reading: 4
Reading: 5
Reading: 6
Reading: 7
Reading: 8
Reading: 9
Finished reading!