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Question

I'm trying to pass the results of munging a slice into a channel. Here's the obviously broken version. I've tried a few ways of doing it that don't seem to work well. I'm looking for an idiomatic way of tackling this.

func gen() <-chan []int {
    c := make(chan []int)

    go func(c chan []int) {
        defer close(c)
        s := []int{0, 1, 2, 3}

        for i := 0; i < len(s); i++ {
            s[i] = -1
            c <- s
        }
    }(c)

    return c

}

func main() {
    for s := range gen() {
        fmt.Println(s)
    }
}

Result:

[-1 -1 2 3]
[-1 -1 2 3]
[-1 -1 -1 -1]
[-1 -1 -1 -1]

Answer 1

It does not work because the underlying array is the same. So you are modifying the same memory.

Here is a working example. Copy the memory at each round.

http://play.golang.org/p/OXfKVg8ZlZ

package main

import "fmt"

func gen() <-chan []int {
    c := make(chan []int)

    go func(c chan []int) {
        defer close(c)

        s := []int{0, 1, 2, 3}
        for i := 0; i < len(s); i++ {
            s[i] = -1
            newSlice := make([]int, len(s))
            copy(newSlice, s)
            c <- newSlice
        }
    }(c)

    return c

}

func main() {
    for s := range gen() {
        fmt.Println(s)
    }
}

Output

[-1 1 2 3]
[-1 -1 2 3]
[-1 -1 -1 3]
[-1 -1 -1 -1]