David,
There's a good argument for not spending time adding this to the spec and
compilers: there are bigger issues for the existing language developers.
Jason,
I've suggested the non-receiving assignment is set to the zero value, ok
only applies to the receiving assignment and can be used twice since both
are bool, and yes there are a lot of commas. Perhaps there could be special
syntax for the multiple ok:
select{
case x := <-c1, y := <-c2, (ok):
// ok is for whichever is assigned or closed
}
Maybe living with the commas isn't too bad:
select{
case x, ok := <-c1, y, ok := <-c2, z, ok := <-c3:
// ok is for whichever is assigned or closed
}
Or how about ;? Two examples:
select{
case x, ok := <-c1; y, ok := <-c2:
if ok == false {
return
}
if x != false {
fmt.Println("true on c1")
break
}
fmt.Printf("non-zero %v on c2\n", y)
case x, ok := <-c3; y, ok := <-c4:
if ok == false {
return
}
if x != 0 {
fmt.Println(x)
} else {
fmt.Println(y)
}
continue
case c5<-v1; c6<-v2; c7<-v3:
break OUTER
}
select{
case x, ok := <-c1
y, ok := <-c2:
if ok == false {
return
}
if x != false {
fmt.Println("true on c1")
break
}
fmt.Printf("%v on c2\n", y)
case x, ok := <-c3
y, ok := <-c4
z := <-c8:
if ok == false {
return
}
if x != 0 {
fmt.Println(x)
} else if y != nil {
fmt.Println(y)
} else {
fmt.Println(z)
}
continue
case c5<-v1
c6<-v2
c7<-v3:
break OUTER
}
ok would be set to true if the receiving assignment does not assign it but
other parallel assignments have it.
Matt
On Friday, December 22, 2017 at 12:44:03 AM UTC-6, Jason Phillips wrote:
>
> Matt,
>
> Would that mean that other receive expression(s) yield the zero value?
>
> select {
> case x := <-c1, y := <-c2:
> // If a value is received from c1, is y the zero value?
> }
>
> Would the multi-valued assignment form of the receive operator gain an
> additional meaning?
>
> select {
> case x, ok := <-c1, y := <-c2:
> // If a value is received from c2, does "ok" designate unsuccessful
> receive or channel close?
> }
>
> Additionally, the commas become awfully confusing with multiple
> multi-valued assignments:
>
> select {
> case x, ok1 := <-c1, y, ok2 := <-c2:
> // Do something
> }
>
>
> Jason
>
> On Thursday, December 21, 2017 at 2:38:02 PM UTC-5, matthe...@gmail.com
> wrote:
>>
>> I would assume only one would send/receive out of the comma list for a
>> case to be executed.
>>
>> Matt
>>
>> On Thursday, December 21, 2017 at 12:32:22 PM UTC-6, Jason Phillips wrote:
>>>
>>> With a multiple expression switch statement, the associated case is
>>> executed if any expression is equal to the switch expression. For a
>>> multiple expression select, would all channel expressions have to proceed
>>> for the associated case to execute?
>>>
>>> e.g.
>>>
>>> select {
>>> case x := <-c1, y := <-c2:
>>> // is it guaranteed that both c1 and c2 have produced a value, or
>>> just one or the other?
>>> }
>>>
>>> What about send operations?
>>>
>>> select {
>>> case c1 <- 10, c2 <- 20:
>>> // is this only executed if both sends happened?
>>> }
>>>
>>>
>>> Jason
>>>
>>> On Thursday, December 21, 2017 at 9:04:35 AM UTC-5, matthe...@gmail.com
>>> wrote:
>>>>
>>>> First the switch behavior surprised me when looking at how to stack
>>>> cases, but then later I was surprised that select doesn't have the same
>>>> thing. Consistency is the only reason to write it down, my concrete
>>>> example
>>>> doesn't need this as shown by Damien in the proposal.
>>>>
>>>> Matt
>>>>
>>>> On Wednesday, December 20, 2017 at 6:51:36 PM UTC-6, Rob 'Commander'
>>>> Pike wrote:
>>>>>
>>>>> There is no particular reason, it was just to keep things simple, if
>>>>> it was even talked about. I don't think it was.
>>>>>
>>>>> If you want to propose a change, now is a good time to do that. Not
>>>>> sure the idea is above the bar, though.
>>>>>
>>>>> -rob
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Thu, Dec 21, 2017 at 9:39 AM, <matthe...@gmail.com> wrote:
>>>>>
>>>>>> Tracker proposal for this: https://github.com/golang/go/issues/23196
>>>>>>
>>>>>> Matt
>>>>>>
>>>>>> On Monday, December 18, 2017 at 10:11:02 AM UTC-6,
>>>>>> matthe...@gmail.com wrote:
>>>>>>>
>>>>>>> I guess with select you can't do the comma for multiple cases having
>>>>>>> one behavior like with switch:
>>>>>>>
>>>>>>> select{
>>>>>>> case <-c1, <-c2: // gofmt: expected 1 expression
>>>>>>> fmt.Println("c1 or c2")
>>>>>>> case <-c3:
>>>>>>> }
>>>>>>>
>>>>>>> switch s{
>>>>>>> case v1, v2:
>>>>>>> fmt.Println("v1 or v2")
>>>>>>> case v3:
>>>>>>> }
>>>>>>>
>>>>>>> I assume this is because select cases have an optional var
>>>>>>> assignment. This would have been nice for detecting an explicit client
>>>>>>> cancel action versus a w.(http.CloseNotifier).CloseNotify() where the
>>>>>>> resulting server action is the same.
>>>>>>>
>>>>>>> Matt
>>>>>>>
>>>>>> --
>>>>>> You received this message because you are subscribed to the Google
>>>>>> Groups "golang-nuts" group.
>>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>>> send an email to golang-nuts...@googlegroups.com.
>>>>>> For more options, visit https://groups.google.com/d/optout.
>>>>>>
>>>>>
>>>>>
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