go-patterns/concurrency/generator.md

# Generator Pattern

[Generators](https://en.wikipedia.org/wiki/Generator_(computer_programming)) yields a sequence of values one at a time.

## Implementation 

```go
func Count(start int, end int) chan int {
    ch := make(chan int)

    go func(ch chan int) {
        for i := start; i <= end ; i++ {
            // Blocks on the operation
            ch <- i
        }

		close(ch)
	}(ch)

	return ch
}
```

## Usage

```go
fmt.Println("No bottles of beer on the wall")

for i := range Count(1, 99) {
    fmt.Println("Pass it around, put one up,", i, "bottles of beer on the wall")
    // Pass it around, put one up, 1 bottles of beer on the wall
    // Pass it around, put one up, 2 bottles of beer on the wall
    // ...
    // Pass it around, put one up, 99 bottles of beer on the wall
}

fmt.Println(100, "bottles of beer on the wall")
```