在指针接收器上调用 Elem() 方法以进行结构反射的必要性

Question

I have struct

type ChartOpts struct {
    Name              mypakage.MyType
    Repo              mypakage.MyType
}

on which I want to set a receiver for reflection.

func (chartOpts *ChartOpts) BindFlags() {
    fields := reflect.TypeOf(chartOpts)
    values := reflect.ValueOf(chartOpts)
    num := fields.NumField()
    fmt.Println(fields, values, num)
}

The above code panics

panic: reflect: NumField of non-struct type *app.ChartOpts

Why do I need to call the Elem() method to fix this?

func (chartOpts *ChartOpts) BindFlags() {
    fields := reflect.TypeOf(chartOpts)
    values := reflect.ValueOf(chartOpts)
    num := fields.Elem().NumField()
    fmt.Println(fields, values, num)
}

Answer 1

Because type of chartOpts is *ChartOpts , a pointer to ChartOpts type. Pointers have no fields, only structs. Calling Elem() on its type descriptor will return a type descriptor that represents / describes ChartOpts , a struct type which does have fields.