Type.GetGenericTypeDefinition Method
Definition
Important
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Returns a Type object that represents a generic type definition from which the current generic type can be constructed.
public:
abstract Type ^ GetGenericTypeDefinition();public:
virtual Type ^ GetGenericTypeDefinition();public abstract Type GetGenericTypeDefinition ();public virtual Type GetGenericTypeDefinition ();abstract member GetGenericTypeDefinition : unit -> Typeabstract member GetGenericTypeDefinition : unit -> Type
override this.GetGenericTypeDefinition : unit -> TypePublic MustOverride Function GetGenericTypeDefinition () As TypePublic Overridable Function GetGenericTypeDefinition () As TypeReturns
A Type object representing a generic type from which the current type can be constructed.
Exceptions
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.
Examples
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<TKey,TValue> type; the constructed type represents a Dictionary<TKey,TValue> of Test objects with string keys.
using namespace System;
using namespace System::Reflection;
using namespace System::Collections::Generic;
public ref class Test
{
public:
static void Main()
{
Console::Write( L"\r\n--- Get the generic type that " );
Console::WriteLine( L"defines a constructed type." );
// Create a Dictionary of Test objects, using strings for the
// keys.
Dictionary< String^,Test^ >^ d = gcnew Dictionary< String^,Test^ >;
// Get a Type object representing the constructed type.
//
Type^ constructed = d->GetType();
DisplayTypeInfo( constructed );
Type^ myGeneric = constructed->GetGenericTypeDefinition();
DisplayTypeInfo( myGeneric );
}
private:
static void DisplayTypeInfo( Type^ t )
{
Console::WriteLine( L"\r\n{0}", t );
Console::WriteLine( L"\tIs this a generic type definition? {0}",
t->IsGenericTypeDefinition );
Console::WriteLine( L"\tIs it a generic type? {0}",
t->IsGenericType );
array<Type^>^typeArguments = t->GetGenericArguments();
Console::WriteLine( L"\tList type arguments ({0}):",
typeArguments->Length );
System::Collections::IEnumerator^ myEnum =
typeArguments->GetEnumerator();
while ( myEnum->MoveNext() )
{
Type^ tParam = safe_cast<Type^>(myEnum->Current);
Console::WriteLine( L"\t\t{0}", tParam );
}
}
};
int main()
{
Test::Main();
}
/* 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
*/
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
*/
open System
open System.Collections.Generic
type Test() = class end
let displayTypeInfo (t: Type) =
printfn $"\n{t}"
printfn $"\tIs this a generic type definition? {t.IsGenericTypeDefinition}"
printfn $"\tIs it a generic type? {t.IsGenericType}"
let typeArguments = t.GetGenericArguments()
printfn $"\tList type arguments ({typeArguments.Length}):"
for tParam in typeArguments do
printfn $"\t\t{tParam}"
printfn "\n--- Get the generic type that defines a constructed type."
// Create a Dictionary of Test objects, using strings for the keys.
let d = Dictionary<string, Test>()
// Get a Type object representing the constructed type.
let constructed = d.GetType()
displayTypeInfo constructed
let generic = constructed.GetGenericTypeDefinition()
displayTypeInfo generic
(* 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
*)
Imports System.Reflection
Imports System.Collections.Generic
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
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
End Class
' 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
'
Remarks
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
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.
