Type.GetGenericTypeDefinition Method ()


The .NET API Reference documentation has a new home. Visit the .NET API Browser on docs.microsoft.com to see the new experience.

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 Overridable Function GetGenericTypeDefinition As Type

Return Value

Type: System.Type

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

Exception Condition

The current type is not a generic type. That is, IsGenericType returns false.


The invoked method is not supported in the base class. Derived classes must provide an implementation.

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.


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(Of TKey, TValue) type; the constructed type represents a Dictionary(Of TKey, TValue) of Test objects with string keys.

Imports System
Imports System.Reflection
Imports System.Collections.Generic
Imports Microsoft.VisualBasic

Public Class Test
    Public Shared Sub Main() 
        Console.WriteLine(vbCrLf & "--- Get the generic type that defines a constructed type.")

        ' Create a Dictionary of Test objects, using strings for the
        ' keys.
        Dim d As New Dictionary(Of String, Test)

        ' Get a Type object representing the constructed type.
        Dim constructed As Type = d.GetType()

        Dim generic As Type = constructed.GetGenericTypeDefinition()
    End Sub 'Main

    Private Shared Sub DisplayTypeInfo(ByVal t As Type) 
        Console.WriteLine(vbCrLf & t.ToString())
        Console.WriteLine(vbTab & "Is this a generic type definition? " _
            & t.IsGenericTypeDefinition)
        Console.WriteLine(vbTab & "Is it a generic type? " _
            & t.IsGenericType)
        Dim typeArguments As Type() = t.GetGenericArguments()
        Console.WriteLine(vbTab & "List type arguments (" _
            & typeArguments.Length & "):")
        For Each tParam As Type In typeArguments
            Console.WriteLine(vbTab & vbTab & tParam.ToString())
        Next tParam
    End Sub 'DisplayTypeInfo
End Class 'Test

' This example produces the following output:
'--- Get the generic type that defines a constructed type.
'        Is this a generic type definition? False
'        Is it a generic type? True
'        List type arguments (2):
'                System.String
'                Test
'        Is this a generic type definition? True
'        Is it a generic type? True
'        List type arguments (2):
'                TKey
'                TValue

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
Return to top