GoStringer接口的结构声明如下:
type GoStringer interface {
GoString() string
}
作用:实现了GoStringer接口的类型(即有GoString方法),定义了该类型值的go语法表示。当采用verb %#v格式化一个操作数时,会调用GoString方法来生成输出的文本。
package main
import (
"fmt"
)
type Address struct {
City string
State string
Country string
}
type Person struct {
Name string
Age uint
Addr *Address
}
// 实现GoStringer接口的GoString方法,输出一个合适的字符串当调用%#v时
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.",
},
}
//如果没有实现GoString()方法,则fmt.Printf("%#v\n",p1)的默认输出是
// Person{Name:"Warren", Age:0x1f, Addr:(*main.Address)(0x10448240)}
//0x10448240 只是表示这是一个结构体地址。不是固定值
fmt.Printf("%#v\n", p1)
//结果输出为:
//Person{Name: "Warren", Age: 31, Addr: &Address{City: "Denver", State: "CO", Country: "U.S.A."}}
p2 := Person{
Name: "Theia",
Age: 4,
}
//如果没有实现GoString()方法,则fmt.Printf("%#v\n",p1)的默认输出是
// Person{Name:"Theia", Age:0x4, Addr:(*main.Address)(nil)}
fmt.Printf("%#v\n", p2)
//结果输出为:
//Person{Name: "Theia", Age: 4}
}