The type 'string' must be a non-nullable type in order to use it as parameter T in the generic type or method 'System.Nullable<T>'

Asked 2012-02-10T23:51:46.383

188

Why do I get Error "The type 'string' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'System.Nullable'"?

using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using Universe;

namespace Universe
{
    public class clsdictionary
    {
      private string? m_Word = "";
      private string? m_Meaning = "";

      string? Word { 
          get { return m_Word; }
          set { m_Word = value; }
      }

      string? Meaning { 
          get { return m_Meaning; }
          set { m_Meaning = value; }
      }
    }
}

c# nullable

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1 Answer

string is a reference type, a class. You can only use Nullable<T> or the T? C# syntactic sugar with non-nullable value types such as int and Guid.

In particular, as string is a reference type, an expression of type string can already be null:

string lookMaNoText = null;

answered 2012-02-10T23:53:05.803

The type 'string' must be a non-nullable type in order to use it as parameter T in the generic type or method 'System.Nullable<T>'

1 Answer

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