go - 菊花链输入，输出 channel 一起在golang中

Question

我有以下接口(interface)和结构

type PiplineStep interface {
    Do(ctx context.Context, in <-chan Message) (<-chan Message, <-chan error, error)
}

type Pipline struct {
    Steps []core.PiplineStep
}

现在我正在尝试菊花接口(interface)来创建如下所示的管道

    for _, step := range p.Steps {
        out, errc, err := step.Do(ctx, out)
        errcList = append(errcList, errc)

        if err != nil {
            errc <- err
            return
        }

        select {
        case outer <- msg:
        case <-ctx.Done():
            return
        }
    }

但是编译器说不，这可能吗？

我收到以下错误“out declared and not used”我已尝试遵循，但似乎所有步骤都收到相同的 chan

    for _, step := range p.Steps {
        var tmpOut <-chan core.Message
        tmpOut = out
        tmpOut, errcTmp, err := step.Do(ctx, tmpOut)
        errcList = append(errcList, errcTmp)

        if err != nil {
            errc <- err
            return
        }
        select {
        case out <- msg:
        case <-ctx.Done():
            return
        }
    }

Answer 1

如果你想在每次迭代中重复使用它，你必须在循环外声明你的 channel 变量(为简洁起见省略了错误和上下文):

package main

import "fmt"

func main() {
    var pipeline Pipeline

    pipeline.Steps = append(pipeline.Steps,
            AddBang{},
            AddBang{},
            AddBang{},
    )

    src := make(chan Message)
    pipe := src

    for _, s := range pipeline.Steps {
            pipe = s.Do(pipe)
    }

    go func() {
            src <- "msg 1"
            src <- "msg 2"
            src <- "msg 3"
    }()

    fmt.Println(<-pipe)
    fmt.Println(<-pipe)
    fmt.Println(<-pipe)
}

type Message string

type Pipeline struct {
    Steps []PipelineStep
}

type PipelineStep interface {
    Do(in chan Message) chan Message
}

type AddBang struct{}

func (AddBang) Do(in chan Message) chan Message {
    out := make(chan Message)
    go func() {
            defer close(out)
            for m := range in {
                    out <- m + "!"
            }
    }()
    return out
}

在 Playground 上试试:https://play.golang.org/p/ItVLUBRpNA1