golang练习：方法中缺少图像

Question

I am wokring through the exercise:images at https://tour.golang.org/methods/25 and I have run into a problem. Here is my code...

package main

import (
    "golang.org/x/tour/pic"
    "image"
)

type Image struct{
    image *image.RGBA   
}

func main() {
    rect := image.Rect(0,0,255,255)
    myImage := image.NewRGBA(rect)
    m := Image{myImage}
    pic.ShowImage(m)
}

it gives me the error...

tmp/sandbox089594299/main.go:16: cannot use m (type Image) as type image.Image in argument to pic.ShowImage:
Image does not implement image.Image (missing At method)

But image.NewRGBA returns a *NRGBA and that does indeed have an At() method. Also I assume since the At() method is the last method required by the image.Image interface then it is finding the other two required methods...so what is up with the At()?

image.NRGBA: https://golang.org/pkg/image/#NRGBA

image.Image interface: https://golang.org/pkg/image/#Image

Answer 1

Your type Image does not implement the At method. If you want your type to inherit the methods implemented by *image.RGBA, use an anonymous field:

type Image struct{
     *image.RGBA   
}

See https://golang.org/doc/effective_go.html#embedding.