MethodInfo.MakeGenericMethod Method (Type())


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Substitutes the elements of an array of types for the type parameters of the current generic method definition, and returns a MethodInfo object representing the resulting constructed method.

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

Public Overridable Function MakeGenericMethod (
	ParamArray typeArguments As Type()
) As MethodInfo


Type: System.Type()

An array of types to be substituted for the type parameters of the current generic method definition.

Return Value

Type: System.Reflection.MethodInfo

A MethodInfo object that represents the constructed method formed by substituting the elements of typeArguments for the type parameters of the current generic method definition.

Exception Condition

The current MethodInfo does not represent a generic method definition. That is, IsGenericMethodDefinition returns false.


typeArguments is null.


Any element of typeArguments is null.


The number of elements in typeArguments is not the same as the number of type parameters of the current generic method definition.


An element of typeArguments does not satisfy the constraints specified for the corresponding type parameter of the current generic method definition.


This method is not supported.

The MakeGenericMethod method allows you to write code that assigns specific types to the type parameters of a generic method definition, thus creating a MethodInfo object that represents a particular constructed method. If the ContainsGenericParameters property of this MethodInfo object returns true, you can use it to invoke the method or to create a delegate to invoke the method.

Methods constructed with the MakeGenericMethod method can be open, that is, some of their type arguments can be type parameters of enclosing generic types. You might use such open constructed methods when you generate dynamic assemblies. For example, consider the following C#, Visual Basic, and C++ code.

class C
    T N<T,U>(T t, U u) {...}
    public V M<V>(V v)
        return N<V,int>(v, 42);

Class C
    Public Function N(Of T,U)(ByVal ta As T, ByVal ua As U) As T
    End Function
    Public Function M(Of V)(ByVal va As V ) As V
        Return N(Of V, Integer)(va, 42)
    End Function
End Class

ref class C
    generic <typename T, typename U> T N(T t, U u) {...}
    generic <typename V> V M(V v)
        return N<V, int>(v, 42);

The method body of M contains a call to method N, specifying the type parameter of M and the type Int32. The IsGenericMethodDefinition property returns false for method N<V,int>. The ContainsGenericParameters property returns true, so method N<V,int> cannot be invoked.

For a list of the invariant conditions for terms specific to generic methods, see the IsGenericMethod property. For a list of the invariant conditions for other terms used in generic reflection, see the IsGenericType property.

The following code example demonstrates the properties and methods of MethodInfo that support the examination of generic methods. The example does the following:

  • Defines a class that has a generic method.

  • Creates a MethodInfo that represents the generic method.

  • Displays properties of the generic method definition.

  • Assigns type arguments to the type parameters of the MethodInfo, and invokes the resulting constructed generic method.

  • Displays properties of the constructed generic method.

  • Retrieves the generic method definition from the constructed method and compares it to the original definition.

Imports System
Imports System.Reflection

' Define a class with a generic method.
Public Class Example
    Public Shared Sub Generic(Of T)(ByVal toDisplay As T)
        Console.WriteLine(vbCrLf & "Here it is: {0}", toDisplay)
    End Sub
End Class

Public Class Test
    Public Shared Sub Main() 
        Console.WriteLine(vbCrLf & "--- Examine a generic method.")

        ' Create a Type object representing class Example, and
        ' get a MethodInfo representing the generic method.
        Dim ex As Type = GetType(Example)
        Dim mi As MethodInfo = ex.GetMethod("Generic")


        ' Assign the Integer type to the type parameter of the Example 
        ' method.
        Dim arguments() As Type = { GetType(Integer) }
        Dim miConstructed As MethodInfo = mi.MakeGenericMethod(arguments)


        ' Invoke the method.
        Dim args() As Object = { 42 }
        miConstructed.Invoke(Nothing, args)

        ' Invoke the method normally.
        Example.Generic(Of Integer)(42)

        ' Get the generic type definition from the constructed method,
        ' and show that it's the same as the original definition.
        Dim miDef As MethodInfo = miConstructed.GetGenericMethodDefinition()
        Console.WriteLine(vbCrLf & "The definition is the same: {0}", _
            miDef Is mi)
    End Sub 'Main

    Private Shared Sub DisplayGenericMethodInfo(ByVal mi As MethodInfo) 
        Console.WriteLine(vbCrLf & mi.ToString())

        Console.WriteLine(vbTab _
            & "Is this a generic method definition? {0}", _

        Console.WriteLine(vbTab & "Is it a generic method? {0}", _

        Console.WriteLine(vbTab _
            & "Does it have unassigned generic parameters? {0}", _

        ' If this is a generic method, display its type arguments.
        If mi.IsGenericMethod Then
            Dim typeArguments As Type() = mi.GetGenericArguments()

            Console.WriteLine(vbTab & "List type arguments ({0}):", _

            For Each tParam As Type In typeArguments
                ' IsGenericParameter is true only for generic type
                ' parameters.
                If tParam.IsGenericParameter Then
                    Console.WriteLine(vbTab & vbTab _
                        & "{0}  parameter position: {1}" _
                        & vbCrLf & vbTab & vbTab _
                        & "   declaring method: {2}", _
                        tParam,  _
                        tParam.GenericParameterPosition, _
                    Console.WriteLine(vbTab & vbTab & tParam.ToString())
                End If
            Next tParam
        End If
    End Sub 
End Class 

' This example produces the following output:
'--- Examine a generic method.
'Void Generic[T](T)
'        Is this a generic method definition? True
'        Is it a generic method? True
'        Does it have unassigned generic parameters? True
'        List type arguments (1):
'                T  parameter position: 0
'                   declaring method: Void Generic[T](T)
'Void Generic[Int32](Int32)
'        Is this a generic method definition? False
'        Is it a generic method? True
'        Does it have unassigned generic parameters? False
'        List type arguments (1):
'                System.Int32
'Here it is: 42
'Here it is: 42
'The definition is the same: True

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
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