Question

Can I create an automatic generic helper method? Let me explain.

This is how I do now:

item.slp_spot_lang_prop.GetAvailable<slp_spot_lang_prop>(Model.LanguageAlternatives).slp_title

And then I have this helper method

public static T GetAvailable<T>(this IEnumerable<ILanguageEntity> helper, IQueryable<langa_language_alternative> languageAlt)
{     
  return (T) helper.SingleOrDefault(d => d.LanguageId == languageAlt.Single(e => e.langa_sitent_id == (int)d.SiteEntityId && e.langa_entid == d.EntityId && e.langa_wantedlangid == Global.SiteInfo.LanguageID).langa_availablelangid);
}

What I want to be able to do is simply

item.slp_spot_lang_prop.GetAvailable(Model.LanguageAlternatives).slp_title

And something like:

public static GetAvailable(this IEnumerable<ILanguageEntity> helper, IQueryable<langa_language_alternative> languageAlt)
{     
  var type = helper.GetEnumerator().Current.GetType().BaseType;
  return (type) helper.SingleOrDefault(d => d.LanguageId == languageAlt.Single(e => e.langa_sitent_id == (int)d.SiteEntityId && e.langa_entid == d.EntityId && e.langa_wantedlangid == Global.SiteInfo.LanguageID).langa_availablelangid);
}

I hope you understand what I mean. The returning type should be an singular of the IEnumerable<IlanguageEntity>‘s basetype which in the example should be slp_spot_lang_prop.

The whole purpose is to get rid of the GetAvailable<type>() and just have GetAvailable(), since it is an helper method I know already the return type.

Answer 1

Have you tried using a constraint on the generic to specify the helper type (it’s not a helper, but you know this)? Using the constraint forces T to be, derive from, or implement the constraint type, but allows the actual value of T to be induced from the argument instead of specified. In your previous declaration, it had no way to determine what T was since it was unrelated to any of the parameters.

public static T GetAvailable<T>(this IEnumerable<T> helper,
                                IQueryable<langa_language_alternative> languageAlt)
   where T : ILanguageEntity
{     
  return (T) helper.SingleOrDefault(d => d.LanguageId == languageAlt.Single(e => e.langa_sitent_id == (int)d.SiteEntityId
                                         && e.langa_entid == d.EntityId
                                         && e.langa_wantedlangid == Global.SiteInfo.LanguageID).langa_availablelangid);
}