Ju's coding note

修改別人寫的代碼時出現一個奇怪的錯誤， 模擬代碼如下:

package main

import "fmt"

func main(){
	phone:= NewPhone("Tom")
	var caller PhoneFeatures = phone
	caller.Call()
}

type Phone struct{
	UserName string
}

func NewPhone(userName string) Phone {
	return Phone{UserName: userName}
}

func (p *Phone) Call()  {
    fmt.Println(p.UserName," Call...")
}

type PhoneFeatures interface{
	Call()
}

執行以上程式碼在轉型成interface時會出現錯誤:

乍看之下很奇怪，Call方法已經有被實現，卻跳出錯誤沒有被實現
而修復的方式有兩種:

1. 將constructor回傳value改為pointer

   func NewPhone(userName string) *Phone {
   	return &Phone{UserName: userName}
   }

    

2. 或改利用value receiver實現Call()

   func (p Phone) Call()  {
       fmt.Println(p.UserName," Call...")
   }

    

這時候進一步的疑問就來了，如果constructor回傳pointer搭配value實現interface，結果會是甚麼?

func NewPhone(userName string) *Phone {
	return &Phone{UserName: userName}
}

func (p Phone) Call()  {
    fmt.Println(p.UserName," Call...")
}

修改後執行一切正常，小結如下:

	implementing interface By
	value receiver	pointer receiver
constructor returns values	ok	error
constructor returns pointers	ok	ok

所以constructor還是返回pointer吧~