指针&Go 中的接口 [英] Pointers & Interfaces in Go

问题描述

我试图了解我在这里做错了什么......感谢所有回复:)

I'm trying to understand what I'm doing wrong here.. all responses appreciated :)

如果取消注释//grow()"有效，

If uncomment "// grow()" works,

其他错误:

prog.go:38:2: 不可能类型 switch case:p(类型植物)不能有动态类型 plant1(grow 方法有指针接收器) prog.go:39:16:不可能的类型断言:植物 1 没有实现植物(生长方法有指针接收器) prog.go:40:2: 不可能的类型切换案例:p(类型植物)不能有动态类型植物2(生长方法有指针接收器) prog.go:41:16: 不可能的类型断言:plant2不实现植物(grow 方法有指针接收器)prog.go:60:12: 不能在参数中使用 p1(植物 1 类型)作为植物类型to showHeight: plant1 没有实现植物(grow 方法有指针接收器) prog.go:61:12: 不能使用 p2 (type plant2) 作为类型在 showHeight 的参数中种植植物:植物 2 不实现植物(grow 方法有指针接收器)

prog.go:38:2: impossible type switch case: p (type plant) cannot have dynamic type plant1 (grow method has pointer receiver) prog.go:39:16: impossible type assertion: plant1 does not implement plant (grow method has pointer receiver) prog.go:40:2: impossible type switch case: p (type plant) cannot have dynamic type plant2 (grow method has pointer receiver) prog.go:41:16: impossible type assertion: plant2 does not implement plant (grow method has pointer receiver) prog.go:60:12: cannot use p1 (type plant1) as type plant in argument to showHeight: plant1 does not implement plant (grow method has pointer receiver) prog.go:61:12: cannot use p2 (type plant2) as type plant in argument to showHeight: plant2 does not implement plant (grow method has pointer receiver)

https://play.golang.org/p/oMv7LdW85yK

package main

import (
    "fmt"
)

type plant1 struct {
    name   string
    height int
}

type plant2 struct {
    species string
    height  int
}

func (self *plant1) grow() {
    self.height++
}
func (self *plant2) grow() {
    self.height++
}

func (self plant1) getHeight() int {
    return self.height
}
func (self plant2) getHeight() int {
    return self.height
}

type plant interface {
    getHeight() int
    //grow()
}

func showHeight(p plant) {
    switch p.(type) {
    case plant1:
        fmt.Println(p.(plant1).name, `Height = `, p.(plant1).getHeight())
    case plant2:
        fmt.Println(p.(plant2).species, `Height = `, p.(plant2).getHeight())
    }

}

func main() {

    p1 := plant1{
        name:   `Plant 10`,
        height: 1,
    }
    p2 := plant2{
        species:   `Plant 20`,
        height: 1,
    }
    p1.grow()
    p1.grow()
    p2.grow()   

    showHeight(p1)
    showHeight(p2)
}

推荐答案

您包装到接口中的值不可寻址.该值必须是可寻址的，以便在指针接收器上调用方法.grow 方法是用指针接收器声明的.所以编译器看到 plant 接口既不是由 plant1 类型实现的，也不是由 plant2 类型实现的.因此，您不能将 plant1 或 plant2 作为 plant 传递给 showHeight func.并且切换是不可能的，因为 plant 接口的实现不包括 plant1 和 plant2 类型.

The value you wrap into interface isn't addressable. The value have to be addressable to call methods on pointer receivers. The grow methods are declared with pointer receiver. So the compiler sees that plant interface is being implemented neither by plant1 type nor by plant2 type. Thus you can't pass plant1 or plant2 as plant to showHeight func. And the switch is impossible because implementations of plant interface don't include plant1 and plant2 types.

参见 为什么有价值存储在接口中在 Golang 中不可寻址

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