proposal: Go 2: add support for copy from a chan

[mei-rune]

extend copy() function. copy from a buffered chan likes

copy([]T, <- chan T) : int

equal to

 func(dst []T, src <- chan T) : int {
   for idx := 0; idx < len(dst); idx ++ {
     select {
     case a, ok := <- src:
         if !ok {
           return idx
         }
        dst[idx] = a
    default:
        return idx
    }
   }
   return len(dst)
 }

examples:

  c := make(chan int, 100)
  c <- 1
  c <- 2
  c <- 3
 ...

  a := make([]int, 10)
  n := copy(a, c)
  a = a[:n]

My main intent is to make it fast for receive message from chan. Is that possible？

[mattn]

If the channel is already closed, copy should panic. And I wonder this way works as atomic correctly.

[ianlancetaylor]

Does this really come up all that often?

[mei-rune]

@ianlancetaylor for me, yes

[randall77]

What's wrong with using the 14-line function you showed?
Is it just lack of generics? How many different types are you using this for?

[mei-rune]

@randall77 No Generics.

I want better performance. Is that possible？
if no then close.

[ianlancetaylor]

The performance isn't going to be any better if we build this into the runtime, so closing.