Type.IsGenericTypeDefinition Property

July 28, 2014

Gets a value indicating whether the current Type represents a generic type definition, from which other generic types can be constructed.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public virtual bool IsGenericTypeDefinition { get; }

Property Value

Type: System.Boolean
true if the Type object represents a generic type definition; otherwise, false.

A generic type definition is a template from which other types can be constructed. For example, from the generic type definition G<T> (expressed in C# syntax; G(Of T) in Visual Basic or generic <typename T> ref class G in C++) you can construct and instantiate the type G<int> (G(Of Integer) in Visual Basic), by calling the MakeGenericType method with a generic argument list containing the Int32 type. Given a Type object representing this constructed type, the GetGenericTypeDefinition method gets the generic type definition back again.

Use the IsGenericTypeDefinition property to determine whether you can create new types from the current type. If the IsGenericTypeDefinition property returns true, you can call the MakeGenericType method to create new generic types.

For a list of the invariant conditions for terms used in generic reflection, see the IsGenericType property remarks.

The following example displays information about a type, including whether or not it is a generic type definition. Information is displayed for a constructed type, for its generic type definition, and for an ordinary type.


using System;
using System.Reflection;
using System.Collections.Generic;

public class Example
{
   private static void DisplayGenericTypeInfo(System.Windows.Controls.TextBlock outputBlock, Type t)
   {
      outputBlock.Text += String.Format("\r\n{0}", t) + "\n";

      outputBlock.Text += String.Format("\tIs this a generic type definition? {0}",
          t.IsGenericTypeDefinition) + "\n";

      outputBlock.Text += String.Format("\tIs it a generic type? {0}",
          t.IsGenericType) + "\n";

      if (t.IsGenericType)
      {
         // If this is a generic type, display the type arguments.
         //
         Type[] typeArguments = t.GetGenericArguments();

         outputBlock.Text += String.Format("\tList type arguments ({0}):",
             typeArguments.Length) + "\n";

         foreach (Type tParam in typeArguments)
         {
            // If this is a type parameter, display its
            // position.
            //
            if (tParam.IsGenericParameter)
            {
               outputBlock.Text += String.Format("\t\t{0}\t(unassigned - parameter position {1})",
                   tParam,
                   tParam.GenericParameterPosition) + "\n";
            }
            else
            {
               outputBlock.Text += String.Format("\t\t{0}", tParam) + "\n";
            }
         }
      }
   }

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      outputBlock.Text += String.Format("\r\n--- Display information about a constructed type, its") + "\n";
      outputBlock.Text += String.Format("    generic type definition, and an ordinary type.") + "\n";

      // Create a Dictionary of Example objects, using strings for the
      // keys.       
      Dictionary<string, Example> d = new Dictionary<string, Example>();

      // Display information for the constructed type and its generic
      // type definition.
      DisplayGenericTypeInfo(outputBlock, d.GetType());
      DisplayGenericTypeInfo(outputBlock, d.GetType().GetGenericTypeDefinition());

      // Display information for an ordinary type.
      DisplayGenericTypeInfo(outputBlock, typeof(string));
   }
}

/* This example produces the following output:

--- Display information about a constructed type, its
    generic type definition, and an ordinary type.

System.Collections.Generic.Dictionary[System.String,Test]
        Is this a generic type definition? False
        Is it a generic type? True
        List type arguments (2):
                System.String
                Test

System.Collections.Generic.Dictionary[TKey,TValue]
        Is this a generic type definition? True
        Is it a generic type? True
        List type arguments (2):
                TKey    (unassigned - parameter position 0)
                TValue  (unassigned - parameter position 1)

System.String
        Is this a generic type definition? False
        Is it a generic type? False
 */


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

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