Generators are rather familiar objects in Python. Generators supply data on demand. Using Go you can create a generator with a goroutine and a channel. Here the goroutine is an anonymous function within a function, simple to implement.
Creating a generator (golang)
// generator_fib4.go
//
// use a channel to simulate a generator
//
// channels are the pipes that connect concurrent goroutines
// send to channel syntax is "chan <- v"
// receive from channel syntax is "v, status := <-chan"
// (data flows in the direction of the arrow)
// receive status is true unless closed with closed(chan)
//
// more detailed info at:
// http://golang.org/ref/spec#Making_slices_maps_and_channels
// https://golang.org/ref/spec#Receive_operator
// online play at:
// http://play.golang.org/p/8CrOj6lmKe
//
// tested with Go version 1.4.2 by vegaseat 3may2015
package main
import "fmt"
// generator using a channel and a goroutine
func fib(n int) chan int {
// create a channel
c := make(chan int)
// create an anonymous inner function
// keyword "go" starts a goroutine
go func() {
x, y := 0, 1
for k := 0; k < n; k++ {
// send value x to the channel c
c <- x
// swap
x, y = y, x+y
}
// close(c) sets the status of the channel c to false
// and is needed by the for/range loop to end
close(c)
}()
return c
}
func main() {
fmt.Println("A Fibonacci generator via channel/goroutine:")
// function fib() returns a channel
// so fc would be of type "chan int"
fc := fib(13)
fmt.Printf("fc is type %T\n", fc)
for k := range fc {
fmt.Printf("%d ", k)
}
fmt.Println()
}
/*
A Fibonacci generator via channel/goroutine:
fc is type chan int
0 1 1 2 3 5 8 13 21 34 55 89 144
*/
vegaseat
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This explains the generator action a little better ...
// generator_fib5.go
//
// use a channel to simulate a generator
//
// channels are the pipes that connect concurrent goroutines
// send to channel syntax is "chan <- v"
// receive from channel syntax is "v, status := <-chan"
// (data flows in the direction of the arrow)
// receive status is true unless closed with closed(chan)
//
// more detailed info at:
// http://golang.org/ref/spec#Making_slices_maps_and_channels
// https://golang.org/ref/spec#Receive_operator
// online play at:
// http://play.golang.org/p/8kwaqcYWFq
//
// tested with Go version 1.4.2 by vegaseat 4may2015
package main
import "fmt"
// generator using a channel and a goroutine
func fib(n int) chan int {
// create a channel
c := make(chan int)
// create an anonymous inner function
// keyword "go" starts a goroutine
go func() {
x, y := 0, 1
for k := 0; k < n; k++ {
// send value x to the channel c
c <- x
// swap
x, y = y, x+y
}
// close(c) sets the status of the channel c to false
// indicates that the channel is now empty
close(c)
}()
return c
}
func main() {
fmt.Println("A Fibonacci generator via channel/goroutine:")
// function fib() returns a channel
// so fc would be of type "chan int"
fc := fib(30)
fmt.Println("The first 3 Fibonacci numbers:", <-fc, <-fc, <-fc)
fmt.Println("The next 3 Fibonacci numbers:", <-fc, <-fc, <-fc)
fmt.Println("The next 3 Fibonacci numbers:", <-fc, <-fc, <-fc)
fmt.Println("The next 12 Fibonacci numbers:")
for k := 0; k < 12; k++ {
fmt.Printf("%d ", <-fc)
}
fmt.Println()
// as the demand exceeds the 30 numbers a zero value is shown
fmt.Println("The next 12 Fibonacci numbers:")
for k := 0; k < 12; k++ {
fmt.Printf("%d ", <-fc)
}
fmt.Println()
// trap the possible end of supply this way
fmt.Println("The next 12 Fibonacci numbers:")
for k := 0; k < 12; k++ {
val, status := <-fc
if status == false {
fmt.Println("channel empty")
break
}
fmt.Printf("%d ", val)
}
}
/*
A Fibonacci generator via channel/goroutine:
The first 3 Fibonacci numbers: 0 1 1
The next 3 Fibonacci numbers: 2 3 5
The next 3 Fibonacci numbers: 8 13 21
The next 12 Fibonacci numbers:
34 55 89 144 233 377 610 987 1597 2584 4181 6765
The next 12 Fibonacci numbers:
10946 17711 28657 46368 75025 121393 196418 317811 514229 0 0 0
The next 12 Fibonacci numbers:
channel empty
*/
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