C#: Is there any difference between bool? and Nullable<bool> ?

In C# are the nullable primitive types (i.e. bool?) just aliases for their corresponding Nullable<T> type or is there a difference between the two?

From stackoverflow MojoFilter

• A Nullable<T> is a structure consisting of a T and a bit flag indicating whether or not the T is valid. A Nullable<bool> has three possible values: true, false and null.

  Edit: Ah, I missed the fact that the question mark after "bool" was actually part of the type name and not an indicator that you were asking a question :). The answer to your question, then, is "yes, the C# bool? is just an alias for Nullable<bool>".

  spoulson : This didn't answer the question.

  Curt Hagenlocher : Yes, I realized that after seeing your answer. Thanks!
  From Curt Hagenlocher

• Null primitives are just regular primitives wrapped in Nullable. Any appearances to the contrary are just the compiler and syntactical sugar.

  From Will

• A bool is a value type, therefore it can't contain a NULL value. If you wrap any value type with Nullable<>, it will give it that ability. Moreover, access methods to the value change by additional properties HasValue and Value.

  But to the question: Nullable<bool> and bool? are aliases.

  Konrad Rudolph : Why is someone systematically downvoting correct answers?

  Chris Marisic : Even though this comment was from way back it's possible that they felt this answer duplicated other answers so they DV'd?

  spoulson : Apparently I'm not the fastest gun in the west. All the top answers are within a few minutes.
  From spoulson

• There is no difference between bool? b = null and Nullable<bool> b = null. The ? is just C# compiler syntax sugar.

  From samjudson

• To access the value of the bool? you need to do the following:

  bool? myValue = true;
  bool hasValue = false;
  
  if (myValue.HasValue && myValue.Value)
  {
    hasValue = true;
  }
  

  Note you can't just do:

  if (myValue)
  {
    hasValue = true;
  }
  

  rohancragg : hmm, not sure whether or not to up-vote this as it doesnt answer the question but it's useful and succinct nonetheless! ;-)

  Mark Ingram : Well, according to Joel you should up-vote if you find it useful - not neccessarily if it's the answer. But then I would say that ;)
  From Mark Ingram

• If you look at the IL using ILDasm, you'll find that they both compile down to Nullable<>.

  From Steve Morgan

• No there is no difference. In summary:

  System.Boolean -> valid values : true, false

  bool -> alias for System.Boolean

  Nullable<bool> -> valid values : true, false, null

  bool? -> alias for Nullable<bool>

  Hope this helps.

  From morechilli