export type TFormFieldsUnion = TFormField<string> | TFormField<boolean> | TFormField<number>
const field1: TFormField<string> = {}
const field2: TFormField<number> = {}
// Array
const fields_a: TFormFieldsUnion[] = [field1, field2]
// Object
const fields_o: { [key: string]: TFormFieldsUnion } = { field1, field2 }