golang fmt包GoStringer接口測試實例

GoStringer接口的結構聲明如下：

type GoStringer interface {
    GoString() string
}

作用：實現了GoStringer接口的類型（即有GoString方法），定義了該類型值的go語法表示。當採用verb %#v格式化一個操作數時，會調用GoString方法來生成輸出的文本。

package main

import (
	"fmt"
)

type Address struct {
	City    string
	State   string
	Country string
}

type Person struct {
	Name string
	Age  uint
	Addr *Address
}

// 實現GoStringer接口的GoString方法，輸出一個合適的字符串當調用%#v時
func (p Person) GoString() string {
	if p.Addr != nil {
		return fmt.Sprintf("Person{Name: %q, Age: %d, Addr: &Address{City: %q, State: %q, Country: %q}}", p.Name, int(p.Age), p.Addr.City, p.Addr.State, p.Addr.Country)
	}
	return fmt.Sprintf("Person{Name: %q, Age: %d}", p.Name, int(p.Age))
}

func main() {
	p1 := Person{
		Name: "Warren",
		Age:  31,
		Addr: &Address{
			City:    "Denver",
			State:   "CO",
			Country: "U.S.A.",
		},
	}

    //如果沒有實現GoString()方法，則fmt.Printf("%#v\n",p1)的默認輸出是
	// Person{Name:"Warren", Age:0x1f, Addr:(*main.Address)(0x10448240)}
    //0x10448240 只是表示這是一個結構體地址。不是固定值
	fmt.Printf("%#v\n", p1)
    //結果輸出爲:
    //Person{Name: "Warren", Age: 31, Addr: &Address{City: "Denver", State: "CO", Country: "U.S.A."}}

	p2 := Person{
		Name: "Theia",
		Age:  4,
	}

    //如果沒有實現GoString()方法，則fmt.Printf("%#v\n",p1)的默認輸出是
	// Person{Name:"Theia", Age:0x4, Addr:(*main.Address)(nil)}
	fmt.Printf("%#v\n", p2)
    //結果輸出爲: 
    //Person{Name: "Theia", Age: 4}
}