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Type.GetGenericTypeDefinition Method

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)
'Declaration
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.
ExceptionCondition
InvalidOperationException

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

NotSupportedException

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.

Important 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(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()
        DisplayTypeInfo(constructed)

        Dim generic As Type = constructed.GetGenericTypeDefinition()
        DisplayTypeInfo(generic)
    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.
'
'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
' 


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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