C# what does the "? " symbol do when it's placed after a generic parameter

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C# What does the "?" symbol do when it's placed after a generic parameter

I've come across this code:

C#

public static Task<long?> GetPageLength() 
{
   // Code 
   ...
}

What I have tried:

Googling but didn't find any information.

Posted 14-Apr-18 1:21am

The_Unknown_Member

Updated 14-Apr-18 2:29am

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OriginalGriff · Accepted Answer · 2018-04-14T02:30:00

The question mark indicates it's not a long any more, but a nullable long.
As you know, long variables are value types, and value types cannot contain null - so you can use the question mark to create a special version of a value type that can also contain null: Nullable Types (C# Programming Guide) | Microsoft Docs[^]