go 类型练习

package mainimport (    "fmt"    "math")type rect struct {    width, height float32}type cir struct {    r float32}type myInt int64func (a myInt) area() myInt {    return a}func (a *rect) area() float32 {    a.height = 12    return (*a).height * (*a).width}func (a cir) area() float32 {    a.r = 1    return (a).r * (a).r * math.Pi}func main() {    r1 := rect{10, 10}    r2 := cir{10}    r3 := myInt(999)    fmt.Println(r1.area())    fmt.Println(r2.area())    fmt.Println(r3.area())    fmt.Println("Hello World")    fmt.Println(r1.height)    fmt.Println(r2.r)}