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package main
import (
func gen(ctx context.Context) <-chan int {
ch := make(chan int)
go func() {
var n int
for {
select {
case <-ctx.Done():
case ch <- n:
return ch
func main() {
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
for n := range gen(ctx) {
if n == 5 {
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Hi Jaana, thanks so much for putting all these together. I'd like to ask a question in regards to the above and your post

We can avoid the problem by signalling the internal goroutine with a stop channel but there is a better solution: cancellable contexts.

Can you explain to me why it's better to pass a context to the gen() function rather than a stop chan struct{}? The gen function would still have the same method changes, both ways will use a single dependency and the stop can also be deferred to ensure no goroutine leaks.

Is this just a new convention? Is there a performance gain to using the context instead? Any thoughts would be most welcome =]
Thanks Kyle

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Xeoncross commented Jul 29, 2017

@KyleHQ, looks like the process is more about handling passing channels over a number of functions (some of which may be third party) like when dealing with a HTTP request:

Still looks like a standard stop chan struct{} would work, but the context can also pass additional values all the way through so it combines a signaler + values.

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gerep commented Nov 24, 2017

Is it required to call cancel() inside the n == 5 conditional even when you are using break to escape the loop and using defer cancel()?

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@gerep It is duplicated I believe.
check the example of WithCancel doc:

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