code: func SandboxContainerWalker(out *Sandbox, containerID string) SandboxWalker {
  	return func(sb Sandbox) bool {
  		if sb.ContainerID() == containerID {
  			*out = sb
  			return true
  		}
  		return false
  	}
  }
docs: // SandboxContainerWalker returns a Sandbox Walker function which looks for an existing Sandbox with the passed containerID