gistfile1.txt

package main

import (
	"fmt"
	"time"

	"golang.org/x/net/context"
)

func leafFunc(ctx context.Context) string {
	ch := make(chan string)
	go func() {
		time.Sleep(time.Second * 2) // 2秒でhelloが返る
		ch <- "hello"
	}()

	select {
	case <-ctx.Done(): // 途中でキャンセルできる
		return "done"
	case resp := <-ch:
		return resp
	}
}

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	cancel()
	resp := leafFunc(ctx)
	fmt.Println(resp)
}