任意個のオプションを渡す

main.go

package main

import "fmt"

func main() {
        Connect(Url("http://hoge.com"))
}

func Connect(options ...Option) error {
        opts := GetDefaultOptions()

        //{Url: AllowReconnect:true}
        fmt.Printf("%+v\n", opts)

        for _, opt := range options {
                if opt != nil {
                        if err := opt(&opts); err != nil {
                                return err
                        }
                }
        }

        //{Url:http://hoge.com AllowReconnect:true}
        fmt.Printf("%+v\n", opts)
        return nil
}

type Options struct {
        Url            string
        AllowReconnect bool
}

func GetDefaultOptions() Options {
        return Options{
                AllowReconnect: true,
        }
}

type Option func(*Options) error

func Url(url string) Option {
        return func(o *Options) error {
                o.Url = url
                return nil
        }
}