count slice length in struct field

I think I need a better solution than my case switch as the struct gains more fields my function will become verbose. Is there a way to swap my switch for a loop?

I have the following code

type Things struct {
	StreetNames    []string `json:"streetNames"`
	Letters        []string `json:"letters"`
	MaleNames      []string `json:"maleNames"`
}

func CheckCategories(data *Things, filePath string) error {
	errMsg := "list has no values or is a missing category in File: " + filePath
	categories := []string{"street_name", "letter", "male_first_name"}
	for _, value := range categories {
		switch value {
		case "street_name":
			if len(data.StreetNames) == 0 {
				return errors.New("street_name " + errMsg)
			}
		case "letter":
			if len(data.Letters) == 0 {
				return errors.New("letter " + errMsg)
			}
		case "male_first_name":
			if len(data.MaleNames) == 0 {
				return errors.New("male_first_name " + errMsg)
			}
		}
	}
	return nil
}

This works for me but the real struct contains 12 fields which makes my functions long and repetitive.

I tried

for _, value := range categories {
		if len("data." + value) == 0 {
			return errors.New(value + errMsg)
}

But when I ran the code I took a moment to notice it wasn't working as intended, Im getting the length of the string. I have tried data[value] but that didn't work either.

> Is there a way to swap my switch for a loop?

You could do the following:

type Things struct {
    StreetNames []string `json:"streetNames"`
    Letters     []string `json:"letters"`
    MaleNames   []string `json:"maleNames"`
}

func CheckCategories(data *Things, filePath string) error {
    errMsg := "list has no values or is a missing category in File: " + filePath
    categories := []struct{
        name  string
        slice []string
    }{
        {"street_name", data.StreetNames},
        {"letter", data.Letters},
        {"male_first_name", data.MaleNames},
    }

    for _, v := range categories {
        if len(v.slice) == 0 {
            return errors.New(v.name + " " + errMsg)
        }
    }
    return nil
}