go 默认参数

package main

import "fmt"

func sum(numbers ...int) int {
    total := 0
    for _, number := range numbers {
        total += number
    }
    return total
}

func main() {
    fmt.Println(sum(1, 2, 3))       // 输出: 6
    fmt.Println(sum(1, 2, 3, 4, 5))  // 输出: 15
}

package main

import "fmt"

type Config struct {
    Port int
    Host string
    Debug bool
}

func main() {
    // 使用零值初始化结构体，模拟默认参数
    config := Config{
        Port: 8080,
        Host: "localhost",
    }
    fmt.Printf("%+v\n", config) // 输出: {Port:8080 Host:localhost Debug:false}
}

package main

import "fmt"

type Config struct {
    Port int
    Host string
    Debug bool
}

type Option func(*Config)

func WithPort(port int) Option {
    return func(c *Config) {
        c.Port = port
    }
}

func WithHost(host string) Option {
    return func(c *Config) {
        c.Host = host
    }
}

func NewConfig(opts ...Option) *Config {
    c := &Config{
        Port: 8080,
        Host: "localhost",
        Debug: false,
    }
    for _, opt := range opts {
        opt(c)
    }
    return c
}

func main() {
    config := NewConfig(WithPort(9090), WithDebug(true))
    fmt.Printf("%+v\n", config) // 输出: {Port:9090 Host:localhost Debug:true}
}