main.go

package main

import "image"

func draw(i *image.Image) {
    //main.go:8: i.Bounds undefined (type *image.Image has no field or method Bounds)
    // But Interface Image says that Bounds has to be
    // implemented.
    i.Bounds()
}

func main() {
    img := image.NewRGBA(123,321)

    /* first try */
    // main.go:13: cannot use img (type *image.RGBA) as type *image.Image in function argument: *image.Image is pointer to interface, not interface
    // me: where is your type inference? Thought there are interfaces for?!?!
    //draw(img)

    /* second */
    // main.go:23: cannot use image.Image(img) (type image.Image) as type *image.Image in function argument:        *image.Image is pointer to interface, not interface
    // me: that sounds logical
    //draw(image.Image(img))

    /* third */
    // main.go:29: cannot convert img (type *image.RGBA) to type *image.Image
    // me: found this solution by gooleling around.
    draw((*image.Image)(img))
}