type Client struct {
  host     string   
  port     string
  timeout  time.Duration
  retryNum int
}

package main

import (
  "fmt"
  "time"
)

type Client struct {
  host     string
  port     string
  timeout  time.Duration
  retryNum int
}

type Option func(*Client)

func NewClient(host, port string, opt ...Option) *Client {
  c := Client{
    host:     host,
    port:     port,
    timeout:  time.Second,
    retryNum: 1,
  }
  for _, option := range opt {
    option(&c)
  }
  return &c
}

func Timeout(timeout time.Duration) Option {
  return func(c *Client) {
    c.timeout = timeout
  }
}

func RetryNum(num int) Option {
  return func(c *Client) {
    c.retryNum = num
  }
}

func main() {
  client := NewClient("localhost", "8080")
}

func main() {
    client := NewClient("localhost", "8080", Timeout(2*time.Second))
}

func main() {
    client := NewClient("localhost", "8080", RetryNum(3))
}

func main() {
    client = NewClient("localhost", "8080", Timeout(2*time.Second), RetryNum(3))
    // 或者
    // client = NewClient("localhost", "8080", RetryNum(3), Timeout(2*time.Second))
}