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Type.GetGenericTypeDefinition Method

Note: This method is new in the .NET Framework version 2.0.

Returns a Type object that represents a generic type definition from which the current generic type can be constructed.

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

public virtual Type GetGenericTypeDefinition ()
public Type GetGenericTypeDefinition ()
public function GetGenericTypeDefinition () : Type

Return Value

A Type object representing a generic type from which the current type can be constructed.

Exception typeCondition

InvalidOperationException

The current type is not a generic type. That is, IsGenericType returns 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). Given a Type object representing this constructed type, the GetGenericTypeDefinition method returns the generic type definition.

If two constructed types are created from the same generic type definition, using the same type arguments, the GetGenericTypeDefinition method returns the same Type object for both types.

If you call the GetGenericTypeDefinition method on a Type object that already represents a generic type definition, it returns the current Type.

NoteImportant:

An array of generic types is not itself generic. In the C# code A<int>[] v; or the Visual Basic code Dim v() As A(Of Integer), the type of variable v is not generic. Use IsGenericType to determine whether a type is generic before calling GetGenericTypeDefinition.

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

The following code example creates an instance of a constructed type by using ordinary instance creation and then uses the GetType and GetGenericTypeDefinition methods to retrieve the constructed type and the generic type definition. This example uses the generic Dictionary type; the constructed type represents a Dictionary of Test objects with string keys.

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

public class Test
{
    public static void Main()
    {
        Console.WriteLine("\r\n--- Get the generic type that defines a constructed type.");

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

        // Get a Type object representing the constructed type.
        //
        Type constructed = d.GetType();
        DisplayTypeInfo(constructed);

        Type generic = constructed.GetGenericTypeDefinition();
        DisplayTypeInfo(generic);
    }

    private static void DisplayTypeInfo(Type t)
    {
        Console.WriteLine("\r\n{0}", t);
        Console.WriteLine("\tIs this a generic type definition? {0}", 
            t.IsGenericTypeDefinition);
        Console.WriteLine("\tIs it a generic type? {0}", 
            t.IsGenericType);
        Type[] typeArguments = t.GetGenericArguments();
        Console.WriteLine("\tList type arguments ({0}):", typeArguments.Length);
        foreach (Type tParam in typeArguments)
        {
            Console.WriteLine("\t\t{0}", tParam);
        }
    }
}

/* This example produces the following output:

--- Get the generic type that defines a constructed type.

System.Collections.Generic.Dictionary`2[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`2[TKey,TValue]
        Is this a generic type definition? True
        Is it a generic type? True
        List type arguments (2):
                TKey
                TValue
 */

import System.*;
import System.Reflection.*;
import System.Collections.Generic.*;

public class Test
{
    public static void main(String[] args)
    {
        Console.WriteLine("\r\n--- Get the generic type that defines "
            + "a constructed type.");
        // Create a Dictionary of Test objects, using Strings for the
        // keys.       
        Dictionary<String,Test> d = new Dictionary<String,Test>();
        // Get a Type object representing the constructed type.
        //
        Type constructed = d.GetType();
        DisplayTypeInfo(constructed);

        Type generic = constructed.GetGenericTypeDefinition();
        DisplayTypeInfo(generic);
    } //main

    private static void DisplayTypeInfo(Type t)
    {
        Console.WriteLine("\r\n{0}", t);
        Console.WriteLine("\tIs this a generic type definition? {0}",
            (System.Boolean)t.get_IsGenericTypeDefinition());
        Console.WriteLine("\tIs it a generic type? {0}",
            (System.Boolean)t.get_IsGenericType());
        Type typeArguments[] = t.GetGenericArguments();
        Console.WriteLine("\tList type arguments ({0}):",
            (Int32)typeArguments.get_Length());
        for (int iCtr = 0; iCtr < typeArguments.get_Length(); iCtr++) {
            Type tParam = (Type)typeArguments.get_Item(iCtr);
            Console.WriteLine("\t\t{0}", tParam);
        }
    } //DisplayTypeInfo
} //Test

/* This example produces the following output:

--- Get the generic type that defines a constructed type.

System.Collections.Generic.Dictionary`2[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`2[TKey,TValue]
        Is this a generic type definition? True
        Is it a generic type? True
        List type arguments (2):
                TKey
                TValue
 */

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

.NET Compact Framework

Supported in: 2.0

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