The feature was in Newsqueak but we deliberately omitted it from Go because
the cost of the operation can be very high and we weren't comfortable
provided such concise notation for such an expensive operation.
-rob
On Fri, Sep 13, 2019 at 4:02 PM Ian Lance Taylor <i...@golang.org> wrote:
> On Thu, Sep 12, 2019 at 9:40 PM Andrey Tcherepanov
> <xnow4fippy...@sneakemail.com> wrote:
> >
> > well, subj - why can't I "just" do a select on a slice of channels?
> Yes, I can run a bunch goroutines with of reads on an each channel, funnel
> it all into 1 notification channel, pick up on the other side... boring
> stuff, really...
> >
> > But why not "just"
> >
> > func main() {
> >
> > cc := make([]chan interface{}, 10)
> >
> > for i := 0; i < len(cc); i++ {
> > cc[i] = make(chan interface{})
> > }
> >
> > dd := make([]chan int)
> >
> > for i := 0; i < 1000; i++ {
> > dd = append(dd, make(chan int))
> > }
> >
> > select {
> >
> > // do we need a special <-[] ?
> > case i, c, v, ok := <-[]cc:
> > fmt.Printf("cc replied : channel index %d, channel %v, value %v,
> ok=%v", i, c, v, ok)
> >
> >
> > // or I dunno, not introducing a new op
> > case i, d, v, ok := <-dd:
> > fmt.Printf("dd sent something: channel index %d, channel %v, value
> %v, ok=%v", i, d, v, ok)
> > }
> >
> > // or shorter, but I hope you get the drift
> >
> > select {
> > case i, c, ok := <-[]cc:
> > fmt.Printf("cc replied : channel index %d, channel %v, value %v,
> ok=%v", i, c, <-c, ok)
> >
> >
> > case i, d, ok := <-dd:
> > fmt.Printf("dd sent something: channel index %d, channel %v, value
> %v, ok=%v", i, d, <-d, ok)
> > }
> > }
> >
> >
> > Why? System limitations? Rarely needed?
> >
> > Feels like extending language to handle that would not be too much of
> violation of an existing code. Ok, lets go nuts! Mirrored "cc <- value" for
> sending to a slice of channels! -- it should pick randomly available
> channel out of the slice of channels!
>
> You actually can do it using the reflect package:
> https://golang.org/pkg/reflect/#Select (not because we necessarily
> want the reflect package to support selecting on a slice of channels,
> but because there is no other reasonable way to write reflect.Select).
>
> It's not in the language proper mainly because it doesn't seem to come
> up very much. I don't think there is even a proposal for it. And
> while anyone is welcome to write a proposal, it will need some
> justification for why it will be worth the cost of complicating the
> language.
>
> Ian
>
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>
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