Confirm struct fields non-zero in Go

Question

I am trying to write a generic function that takes a struct and confirms that the given fields have non-zero values.

This is my function:

func CheckRequiredFields(kind string, i interface{}, fields ...string) error {
    for _, field := range fields {
        value := reflect.ValueOf(i).FieldByName(field)
        if value.Interface() == reflect.Zero(value.Type()).Interface() {
            return fmt.Errorf("missing required %s field %s", kind, field)
        }
    }
    return nil
}

and it works well if a struct is passed in as i, but fails if i is a pointer to a struct.

How can I reflect on the value of an interface if the value passed in is a pointer?

Mr_Pink · Accepted Answer · 2017-02-03 14:17:44Z

1

You can use reflect.Indirect, which returns the value that v points to. If v is a nil pointer, Indirect returns a zero Value. If v is not a pointer, Indirect returns v.

If you want to check if the value was a pointer or not, check it's Kind, and use Elem() to dereference the pointer.

v := reflect.ValueOf(i)
if v.Kind() == reflect.Ptr {
    v = v.Elem()
}

answered Feb 3, 2017 at 14:17

Mr_Pink

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1 Comment

Ralph Over a year ago

Thanks, I thought it would be something like that.

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