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如何:使用反映發出定義泛型型別

本文說明如何建立具有兩個型別參數的簡單泛型型別、如何將類別條件約束、介面條件約束和特殊條件約束套用至型別參數,以及如何建立使用 類別類型參數作為參數類型和傳回型別的成員。

重要

方法不是只因為屬於泛型型別並使用該類型的型別參數,而成為泛型。 方法只有在有自己的類型參數清單時,才會是泛型。 泛型型別上的大部分方法不是泛型,如本例所示。 如需發出泛型方法的範例,請參閱如何︰使用反映發出定義泛型方法

定義泛型類型

  1. 定義名為 GenericEmitExample1 的動態組件。 在本例中,組件在執行後會儲存到磁碟,因此指定 AssemblyBuilderAccess.RunAndSave

    AppDomain^ myDomain = AppDomain::CurrentDomain;
    AssemblyName^ myAsmName = gcnew AssemblyName( L"GenericEmitExample1" );
    AssemblyBuilder^ myAssembly = myDomain->DefineDynamicAssembly( 
        myAsmName, AssemblyBuilderAccess::RunAndSave );
    
    AppDomain myDomain = AppDomain.CurrentDomain;
    AssemblyName myAsmName = new AssemblyName("GenericEmitExample1");
    AssemblyBuilder myAssembly =
        myDomain.DefineDynamicAssembly(myAsmName,
            AssemblyBuilderAccess.RunAndSave);
    
    Dim myDomain As AppDomain = AppDomain.CurrentDomain
    Dim myAsmName As New AssemblyName("GenericEmitExample1")
    Dim myAssembly As AssemblyBuilder = myDomain.DefineDynamicAssembly( _
        myAsmName, _
        AssemblyBuilderAccess.RunAndSave)
    
  2. 定義動態模組。 組件是由可執行模組組成。 組件如僅有一個模組,則模組名稱和組件名稱相同,且檔案名稱是模組名稱加上副檔名。

    ModuleBuilder^ myModule = myAssembly->DefineDynamicModule( 
        myAsmName->Name, String::Concat( myAsmName->Name, L".dll" ) );
    
    ModuleBuilder myModule =
        myAssembly.DefineDynamicModule(myAsmName.Name,
           myAsmName.Name + ".dll");
    
    Dim myModule As ModuleBuilder = myAssembly.DefineDynamicModule( _
        myAsmName.Name, _
        myAsmName.Name & ".dll")
    
  3. 定義類別。 本例中的類別名為 Sample

    TypeBuilder^ myType = myModule->DefineType( L"Sample", 
        TypeAttributes::Public );
    
    TypeBuilder myType =
        myModule.DefineType("Sample", TypeAttributes.Public);
    
    Dim myType As TypeBuilder = myModule.DefineType( _
        "Sample", _
        TypeAttributes.Public)
    
  4. 將包含參數名稱的字串陣列傳遞至 TypeBuilder.DefineGenericParameters 方法,以定義 Sample 的泛型型別參數。 這可讓類別成為泛型型別。 傳回值是代表型別參數的 GenericTypeParameterBuilder 物件陣列,可用於發出的程式碼中。

    在下列程式碼中,Sample 會成為具有型別參數 TFirstTSecond 的泛型型別。 若要讓程式碼便於閱讀,每個 GenericTypeParameterBuilder 都要放在與型別參數同名的變數中。

    array<String^>^typeParamNames = {L"TFirst",L"TSecond"};
    array<GenericTypeParameterBuilder^>^typeParams = 
        myType->DefineGenericParameters( typeParamNames );
    
    GenericTypeParameterBuilder^ TFirst = typeParams[0];
    GenericTypeParameterBuilder^ TSecond = typeParams[1];
    
    string[] typeParamNames = {"TFirst", "TSecond"};
    GenericTypeParameterBuilder[] typeParams =
        myType.DefineGenericParameters(typeParamNames);
    
    GenericTypeParameterBuilder TFirst = typeParams[0];
    GenericTypeParameterBuilder TSecond = typeParams[1];
    
    Dim typeParamNames() As String = {"TFirst", "TSecond"}
    Dim typeParams() As GenericTypeParameterBuilder = _
        myType.DefineGenericParameters(typeParamNames)
    
    Dim TFirst As GenericTypeParameterBuilder = typeParams(0)
    Dim TSecond As GenericTypeParameterBuilder = typeParams(1)
    
  5. 將特殊條件約束新增至型別參數。 在此範例中,型別參數 TFirst 限為具有無參數建構函式的類型及參考型別。

    TFirst->SetGenericParameterAttributes( 
        GenericParameterAttributes::DefaultConstructorConstraint | 
        GenericParameterAttributes::ReferenceTypeConstraint 
    );
    
    TFirst.SetGenericParameterAttributes(
        GenericParameterAttributes.DefaultConstructorConstraint |
        GenericParameterAttributes.ReferenceTypeConstraint);
    
    TFirst.SetGenericParameterAttributes( _
        GenericParameterAttributes.DefaultConstructorConstraint _
        Or GenericParameterAttributes.ReferenceTypeConstraint)
    
  6. 或者將類別和介面條件約束新增至類型參數。 在本例中,型別參數 TFirst 限制為衍生自基底類別的類型,而此基底類別是由包含在變數 baseType 中的 Type 物件所表示;以及實作介面的類型,而此介面的類型包含在變數 interfaceAinterfaceB 中。 請參閱宣告和指派這些變數的程式碼範例。

    array<Type^>^interfaceTypes = { interfaceA, interfaceB };
    TSecond->SetInterfaceConstraints( interfaceTypes );
    TSecond->SetBaseTypeConstraint( baseType );
    
    TSecond.SetBaseTypeConstraint(baseType);
    Type[] interfaceTypes = {interfaceA, interfaceB};
    TSecond.SetInterfaceConstraints(interfaceTypes);
    
    TSecond.SetBaseTypeConstraint(baseType)
    Dim interfaceTypes() As Type = {interfaceA, interfaceB}
    TSecond.SetInterfaceConstraints(interfaceTypes)
    
  7. 定義欄位。 本例中的欄位類型是由型別參數 TFirst 所指定。 GenericTypeParameterBuilder 衍生自 Type,所以只要可以使用類型的位置,都可以使用泛型型別參數。

    FieldBuilder^ exField = 
        myType->DefineField("ExampleField", TFirst, 
            FieldAttributes::Private);
    
    FieldBuilder exField =
        myType.DefineField("ExampleField", TFirst,
            FieldAttributes.Private);
    
    Dim exField As FieldBuilder = _
        myType.DefineField("ExampleField", TFirst, _
            FieldAttributes.Private)
    
  8. 定義使用泛型型別之型別參數的方法。 請注意,這類方法不是泛型,除非它們有自己的型別參數清單。 下列程式碼定義 static 方法 (Visual Basic 為 Shared),其接受 TFirst 陣列並傳回包含陣列所有項目的 List<TFirst> (Visual Basic 為 List(Of TFirst))。 若要定義這個方法,即必須在泛型型別定義 List<T> 呼叫 MakeGenericType,以建立類型 List<TFirst>。 (當您使用 typeof 運算子時會省略 T (Visual Basic 為 GetType),以取得泛型型別定義。) 參數類型是使用 MakeArrayType 方法所建立。

    Type^ listOf = List::typeid;
    Type^ listOfTFirst = listOf->MakeGenericType(TFirst);
    array<Type^>^ mParamTypes = { TFirst->MakeArrayType() };
    
    MethodBuilder^ exMethod = 
        myType->DefineMethod("ExampleMethod", 
            MethodAttributes::Public | MethodAttributes::Static, 
            listOfTFirst, 
            mParamTypes);
    
    Type listOf = typeof(List<>);
    Type listOfTFirst = listOf.MakeGenericType(TFirst);
    Type[] mParamTypes = {TFirst.MakeArrayType()};
    
    MethodBuilder exMethod =
        myType.DefineMethod("ExampleMethod",
            MethodAttributes.Public | MethodAttributes.Static,
            listOfTFirst,
            mParamTypes);
    
    Dim listOf As Type = GetType(List(Of ))
    Dim listOfTFirst As Type = listOf.MakeGenericType(TFirst)
    Dim mParamTypes() As Type = {TFirst.MakeArrayType()}
    
    Dim exMethod As MethodBuilder = _
        myType.DefineMethod("ExampleMethod", _
            MethodAttributes.Public Or MethodAttributes.Static, _
            listOfTFirst, _
            mParamTypes)
    
  9. 發出方法主體。 方法主體中包含三個作業碼,可將輸入陣列載入至堆疊,呼叫接受 IEnumerable<TFirst> (它會執行所有將輸入項目放入清單中的工作) 的 List<TFirst> 建構函式 ,並傳回 (將新的 List<T> 物件留在堆疊上)。 發出此程式碼最困難的部分是取得建構函式。

    GenericTypeParameterBuilder 不支援 GetConstructor 方法,所以不可能直接取得 List<TFirst> 的建構函式。 首先,必須取得泛型型別定義 List<T> 的建構函式,然後呼叫能將它轉換成對應的 List<TFirst> 建構函式的方法。

    此程式碼範例所使用的建構函式接受 IEnumerable<T>。 但是請注意,這不是 IEnumerable<T> 泛型介面的泛型型別定義;相反地,來自 List<T> 的型別參數 T 必須取代 IEnumerable<T> 的型別參數 T。 (這似乎很令人困惑,只因為這兩個類型都有名為 T 的型別參數。這就是這個程式碼範例使用名稱 TFirstTSecond 的原因。)若要取得建構函式引數的類型,請從使用泛型型別定義 IEnumerable<T>,並以 List<T> 的第一個泛型型別參數呼叫 MakeGenericType 開始。 建構函式引數清單必須當成陣列傳遞,本例中只有一個引數。

    注意

    當您在 C# 中使用 typeof 運算子時,泛型型別定義會表示為 IEnumerable<>;在 Visual Basic 中使用 GetType 運算子時,會表示為 IEnumerable(Of )

    現在,在泛型型別定義上呼叫 GetConstructor,即可能取得 List<T> 的建構函式。 若要將此建構函式轉換成對應的 List<TFirst> 的建構函式,請從 List<T>List<TFirst> 和建構函式傳遞至靜態的 TypeBuilder.GetConstructor(Type, ConstructorInfo) 方法。

    ILGenerator^ ilgen = exMethod->GetILGenerator();
         
    Type^ ienumOf = IEnumerable::typeid;
    Type^ TfromListOf = listOf->GetGenericArguments()[0];
    Type^ ienumOfT = ienumOf->MakeGenericType(TfromListOf);
    array<Type^>^ ctorArgs = {ienumOfT};
    
    ConstructorInfo^ ctorPrep = listOf->GetConstructor(ctorArgs);
    ConstructorInfo^ ctor = 
        TypeBuilder::GetConstructor(listOfTFirst, ctorPrep);
    
    ilgen->Emit(OpCodes::Ldarg_0);
    ilgen->Emit(OpCodes::Newobj, ctor);
    ilgen->Emit(OpCodes::Ret);
    
    ILGenerator ilgen = exMethod.GetILGenerator();
    
    Type ienumOf = typeof(IEnumerable<>);
    Type TfromListOf = listOf.GetGenericArguments()[0];
    Type ienumOfT = ienumOf.MakeGenericType(TfromListOf);
    Type[] ctorArgs = {ienumOfT};
    
    ConstructorInfo ctorPrep = listOf.GetConstructor(ctorArgs);
    ConstructorInfo ctor =
        TypeBuilder.GetConstructor(listOfTFirst, ctorPrep);
    
    ilgen.Emit(OpCodes.Ldarg_0);
    ilgen.Emit(OpCodes.Newobj, ctor);
    ilgen.Emit(OpCodes.Ret);
    
    Dim ilgen As ILGenerator = exMethod.GetILGenerator()
    
    Dim ienumOf As Type = GetType(IEnumerable(Of ))
    Dim listOfTParams() As Type = listOf.GetGenericArguments()
    Dim TfromListOf As Type = listOfTParams(0)
    Dim ienumOfT As Type = ienumOf.MakeGenericType(TfromListOf)
    Dim ctorArgs() As Type = {ienumOfT}
    
    Dim ctorPrep As ConstructorInfo = _
        listOf.GetConstructor(ctorArgs)
    Dim ctor As ConstructorInfo = _
        TypeBuilder.GetConstructor(listOfTFirst, ctorPrep)
    
    ilgen.Emit(OpCodes.Ldarg_0)
    ilgen.Emit(OpCodes.Newobj, ctor)
    ilgen.Emit(OpCodes.Ret)
    
  10. 建立類型並儲存檔案。

    Type^ finished = myType->CreateType();
    myAssembly->Save( String::Concat( myAsmName->Name, L".dll" ) );
    
    Type finished = myType.CreateType();
    myAssembly.Save(myAsmName.Name+".dll");
    
    Dim finished As Type = myType.CreateType()
    myAssembly.Save(myAsmName.Name & ".dll")
    
  11. 叫用方法。 ExampleMethod 不是泛型,但它所屬的類型是泛型,因此若要取得 MethodInfo 可以叫用的 ,就必須從的類型定義 Sample建立建構型別。 建構的類型使用符合 TFirst 條件約束的 Example 類別,因為它是參考型別,且有預設的無參數建構函式;也使用符合 TSecond 條件約束的 ExampleDerived 類別。 (ExampleDerived 的程式碼請參見<範例程式碼>一節。)這兩種類型都會傳遞至 MakeGenericType,以建立建構的類型。 然後,使用 GetMethod 方法取得 MethodInfo

    array<Type^>^ typeArgs = 
        { Example::typeid, ExampleDerived::typeid };
    Type^ constructed = finished->MakeGenericType(typeArgs);
    MethodInfo^ mi = constructed->GetMethod("ExampleMethod");
    
    Type[] typeArgs = {typeof(Example), typeof(ExampleDerived)};
    Type constructed = finished.MakeGenericType(typeArgs);
    MethodInfo mi = constructed.GetMethod("ExampleMethod");
    
    Dim typeArgs() As Type = _
        {GetType(Example), GetType(ExampleDerived)}
    Dim constructed As Type = finished.MakeGenericType(typeArgs)
    Dim mi As MethodInfo = constructed.GetMethod("ExampleMethod")
    
  12. 下列程式碼會建立 Example 物件的陣列,將該陣列放在代表要叫用之方法引數的類型 Object 陣列中,並將它們傳遞至 Invoke(Object, Object[]) 方法。 Invoke 方法的第一個引數為 Null 參考,因為方法是 static

    array<Example^>^ input = { gcnew Example(), gcnew Example() };
    array<Object^>^ arguments = { input };
    
    List<Example^>^ listX = 
        (List<Example^>^) mi->Invoke(nullptr, arguments);
    
    Console::WriteLine(
        "\nThere are {0} elements in the List<Example>.", 
        listX->Count);
    
    Example[] input = {new Example(), new Example()};
    object[] arguments = {input};
    
    List<Example> listX =
        (List<Example>) mi.Invoke(null, arguments);
    
    Console.WriteLine(
        "\nThere are {0} elements in the List<Example>.",
        listX.Count);
    
    Dim input() As Example = {New Example(), New Example()}
    Dim arguments() As Object = {input}
    
    Dim listX As List(Of Example) = mi.Invoke(Nothing, arguments)
    
    Console.WriteLine(vbLf & _
        "There are {0} elements in the List(Of Example).", _
        listX.Count _
    )
    

範例

下列程式碼範例會定義名為 Sample 的類別,以及一個基底類別和兩個介面。 程式會為 Sample 定義兩個泛型型別參數,將它轉換成泛型型別。 型別參數是唯一可將類型變成泛型的物件。 程式會顯示定義型別參數之前和之後的測試訊息,以顯示此變化。

使用基底類別和介面的型別參數 TSecond 用於示範類別和介面條件約束,而型別參數 TFirst 用於示範特殊條件約束。

程式碼範例會定義欄位和方法,針對欄位類別和參數使用類別的型別參數,並傳回方法的類型。

建立 Sample 類別之後,即叫用方法。

程式包含兩種方法,一種會列出泛型型別的相關資訊,一種會列出型別參數的特殊條件約束。 這些方法用來顯示已完成之 Sample 類別的相關資訊。

程式會將完成的模組儲存為 磁碟GenericEmitExample1.dll,因此您可以使用 Ildasm.exe (IL 反組譯器) 開啟它,並檢查 類別的 Sample CIL。

using namespace System;
using namespace System::Reflection;
using namespace System::Reflection::Emit;
using namespace System::Collections::Generic;

// Dummy class to satisfy TFirst constraints.
//
public ref class Example {};

// Define a trivial base class and two trivial interfaces 
// to use when demonstrating constraints.
//
public ref class ExampleBase {};
public interface class IExampleA {};
public interface class IExampleB {};

// Define a trivial type that can substitute for type parameter 
// TSecond.
//
public ref class ExampleDerived : ExampleBase, IExampleA, IExampleB {};

// List the constraint flags. The GenericParameterAttributes
// enumeration contains two sets of attributes, variance and
// constraints. For this example, only constraints are used.
//
static void ListConstraintAttributes( Type^ t )
{
   // Mask off the constraint flags. 
   GenericParameterAttributes constraints = 
       t->GenericParameterAttributes & 
       GenericParameterAttributes::SpecialConstraintMask;

   if ((constraints & GenericParameterAttributes::ReferenceTypeConstraint)
           != GenericParameterAttributes::None)
       Console::WriteLine( L"    ReferenceTypeConstraint");

   if ((constraints & GenericParameterAttributes::NotNullableValueTypeConstraint)
           != GenericParameterAttributes::None)
       Console::WriteLine( L"    NotNullableValueTypeConstraint");

   if ((constraints & GenericParameterAttributes::DefaultConstructorConstraint)
           != GenericParameterAttributes::None)
       Console::WriteLine( L"    DefaultConstructorConstraint");
}

static void DisplayGenericParameters( Type^ t )
{
   if (!t->IsGenericType)
   {
       Console::WriteLine( L"Type '{0}' is not generic." );
       return;
   }
   if (!t->IsGenericTypeDefinition)
       t = t->GetGenericTypeDefinition();

   array<Type^>^ typeParameters = t->GetGenericArguments();
   Console::WriteLine( L"\r\nListing {0} type parameters for type '{1}'.", 
       typeParameters->Length, t );

   for each ( Type^ tParam in typeParameters )
   {
       Console::WriteLine( L"\r\nType parameter {0}:", 
           tParam->ToString() );

       for each (Type^ c in tParam->GetGenericParameterConstraints())
       {
           if (c->IsInterface)
               Console::WriteLine( L"    Interface constraint: {0}", c);
           else
               Console::WriteLine( L"    Base type constraint: {0}", c);
       }
       ListConstraintAttributes(tParam);
   }
}

void main()
{
   // Define a dynamic assembly to contain the sample type. The
   // assembly will be run and also saved to disk, so
   // AssemblyBuilderAccess.RunAndSave is specified.
   //
   AppDomain^ myDomain = AppDomain::CurrentDomain;
   AssemblyName^ myAsmName = gcnew AssemblyName( L"GenericEmitExample1" );
   AssemblyBuilder^ myAssembly = myDomain->DefineDynamicAssembly( 
       myAsmName, AssemblyBuilderAccess::RunAndSave );

   // An assembly is made up of executable modules. For a single-
   // module assembly, the module name and file name are the same 
   // as the assembly name. 
   //
   ModuleBuilder^ myModule = myAssembly->DefineDynamicModule( 
       myAsmName->Name, String::Concat( myAsmName->Name, L".dll" ) );

   // Get type objects for the base class trivial interfaces to
   // be used as constraints.
   //
   Type^ baseType = ExampleBase::typeid; 
   Type^ interfaceA = IExampleA::typeid; 
   Type^ interfaceB = IExampleB::typeid;
   
   // Define the sample type.
   //
   TypeBuilder^ myType = myModule->DefineType( L"Sample", 
       TypeAttributes::Public );
   
   Console::WriteLine( L"Type 'Sample' is generic: {0}", 
       myType->IsGenericType );
   
   // Define type parameters for the type. Until you do this, 
   // the type is not generic, as the preceding and following 
   // WriteLine statements show. The type parameter names are
   // specified as an array of strings. To make the code
   // easier to read, each GenericTypeParameterBuilder is placed
   // in a variable with the same name as the type parameter.
   // 
   array<String^>^typeParamNames = {L"TFirst",L"TSecond"};
   array<GenericTypeParameterBuilder^>^typeParams = 
       myType->DefineGenericParameters( typeParamNames );

   GenericTypeParameterBuilder^ TFirst = typeParams[0];
   GenericTypeParameterBuilder^ TSecond = typeParams[1];

   Console::WriteLine( L"Type 'Sample' is generic: {0}", 
       myType->IsGenericType );
   
   // Apply constraints to the type parameters.
   //
   // A type that is substituted for the first parameter, TFirst,
   // must be a reference type and must have a parameterless
   // constructor.
   TFirst->SetGenericParameterAttributes( 
       GenericParameterAttributes::DefaultConstructorConstraint | 
       GenericParameterAttributes::ReferenceTypeConstraint 
   );

   // A type that is substituted for the second type
   // parameter must implement IExampleA and IExampleB, and
   // inherit from the trivial test class ExampleBase. The
   // interface constraints are specified as an array
   // containing the interface types. 
   array<Type^>^interfaceTypes = { interfaceA, interfaceB };
   TSecond->SetInterfaceConstraints( interfaceTypes );
   TSecond->SetBaseTypeConstraint( baseType );

   // The following code adds a private field named ExampleField,
   // of type TFirst.
   FieldBuilder^ exField = 
       myType->DefineField("ExampleField", TFirst, 
           FieldAttributes::Private);

   // Define a static method that takes an array of TFirst and 
   // returns a List<TFirst> containing all the elements of 
   // the array. To define this method it is necessary to create
   // the type List<TFirst> by calling MakeGenericType on the
   // generic type definition, generic<T> List. 
   // The parameter type is created by using the
   // MakeArrayType method. 
   //
   Type^ listOf = List::typeid;
   Type^ listOfTFirst = listOf->MakeGenericType(TFirst);
   array<Type^>^ mParamTypes = { TFirst->MakeArrayType() };

   MethodBuilder^ exMethod = 
       myType->DefineMethod("ExampleMethod", 
           MethodAttributes::Public | MethodAttributes::Static, 
           listOfTFirst, 
           mParamTypes);

   // Emit the method body. 
   // The method body consists of just three opcodes, to load 
   // the input array onto the execution stack, to call the 
   // List<TFirst> constructor that takes IEnumerable<TFirst>,
   // which does all the work of putting the input elements into
   // the list, and to return, leaving the list on the stack. The
   // hard work is getting the constructor.
   // 
   // The GetConstructor method is not supported on a 
   // GenericTypeParameterBuilder, so it is not possible to get 
   // the constructor of List<TFirst> directly. There are two
   // steps, first getting the constructor of generic<T> List and then
   // calling a method that converts it to the corresponding 
   // constructor of List<TFirst>.
   //
   // The constructor needed here is the one that takes an
   // IEnumerable<T>. Note, however, that this is not the 
   // generic type definition of generic<T> IEnumerable; instead, the
   // T from generic<T> List must be substituted for the T of 
   // generic<T> IEnumerable. (This seems confusing only because both
   // types have type parameters named T. That is why this example
   // uses the somewhat silly names TFirst and TSecond.) To get
   // the type of the constructor argument, take the generic
   // type definition generic<T> IEnumerable and 
   // call MakeGenericType with the first generic type parameter
   // of generic<T> List. The constructor argument list must be passed
   // as an array, with just one argument in this case.
   // 
   // Now it is possible to get the constructor of generic<T> List,
   // using GetConstructor on the generic type definition. To get
   // the constructor of List<TFirst>, pass List<TFirst> and
   // the constructor from generic<T> List to the static
   // TypeBuilder.GetConstructor method.
   //
   ILGenerator^ ilgen = exMethod->GetILGenerator();
        
   Type^ ienumOf = IEnumerable::typeid;
   Type^ TfromListOf = listOf->GetGenericArguments()[0];
   Type^ ienumOfT = ienumOf->MakeGenericType(TfromListOf);
   array<Type^>^ ctorArgs = {ienumOfT};

   ConstructorInfo^ ctorPrep = listOf->GetConstructor(ctorArgs);
   ConstructorInfo^ ctor = 
       TypeBuilder::GetConstructor(listOfTFirst, ctorPrep);

   ilgen->Emit(OpCodes::Ldarg_0);
   ilgen->Emit(OpCodes::Newobj, ctor);
   ilgen->Emit(OpCodes::Ret);

   // Create the type and save the assembly. 
   Type^ finished = myType->CreateType();
   myAssembly->Save( String::Concat( myAsmName->Name, L".dll" ) );

   // Invoke the method.
   // ExampleMethod is not generic, but the type it belongs to is
   // generic, so in order to get a MethodInfo that can be invoked
   // it is necessary to create a constructed type. The Example 
   // class satisfies the constraints on TFirst, because it is a 
   // reference type and has a default constructor. In order to
   // have a class that satisfies the constraints on TSecond, 
   // this code example defines the ExampleDerived type. These
   // two types are passed to MakeGenericMethod to create the
   // constructed type.
   //
   array<Type^>^ typeArgs = 
       { Example::typeid, ExampleDerived::typeid };
   Type^ constructed = finished->MakeGenericType(typeArgs);
   MethodInfo^ mi = constructed->GetMethod("ExampleMethod");

   // Create an array of Example objects, as input to the generic
   // method. This array must be passed as the only element of an 
   // array of arguments. The first argument of Invoke is 
   // null, because ExampleMethod is static. Display the count
   // on the resulting List<Example>.
   // 
   array<Example^>^ input = { gcnew Example(), gcnew Example() };
   array<Object^>^ arguments = { input };

   List<Example^>^ listX = 
       (List<Example^>^) mi->Invoke(nullptr, arguments);

   Console::WriteLine(
       "\nThere are {0} elements in the List<Example>.", 
       listX->Count);

   DisplayGenericParameters(finished);
}

/* This code example produces the following output:

Type 'Sample' is generic: False
Type 'Sample' is generic: True

There are 2 elements in the List<Example>.

Listing 2 type parameters for type 'Sample[TFirst,TSecond]'.

Type parameter TFirst:
    ReferenceTypeConstraint
    DefaultConstructorConstraint

Type parameter TSecond:
    Interface constraint: IExampleA
    Interface constraint: IExampleB
    Base type constraint: ExampleBase
 */
using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Collections.Generic;

// Define a trivial base class and two trivial interfaces
// to use when demonstrating constraints.
//
public class ExampleBase {}

public interface IExampleA {}

public interface IExampleB {}

// Define a trivial type that can substitute for type parameter
// TSecond.
//
public class ExampleDerived : ExampleBase, IExampleA, IExampleB {}

public class Example
{
    public static void Main()
    {
        // Define a dynamic assembly to contain the sample type. The
        // assembly will not be run, but only saved to disk, so
        // AssemblyBuilderAccess.Save is specified.
        //
        AppDomain myDomain = AppDomain.CurrentDomain;
        AssemblyName myAsmName = new AssemblyName("GenericEmitExample1");
        AssemblyBuilder myAssembly =
            myDomain.DefineDynamicAssembly(myAsmName,
                AssemblyBuilderAccess.RunAndSave);

        // An assembly is made up of executable modules. For a single-
        // module assembly, the module name and file name are the same
        // as the assembly name.
        //
        ModuleBuilder myModule =
            myAssembly.DefineDynamicModule(myAsmName.Name,
               myAsmName.Name + ".dll");

        // Get type objects for the base class trivial interfaces to
        // be used as constraints.
        //
        Type baseType = typeof(ExampleBase);
        Type interfaceA = typeof(IExampleA);
        Type interfaceB = typeof(IExampleB);

        // Define the sample type.
        //
        TypeBuilder myType =
            myModule.DefineType("Sample", TypeAttributes.Public);

        Console.WriteLine("Type 'Sample' is generic: {0}",
            myType.IsGenericType);

        // Define type parameters for the type. Until you do this,
        // the type is not generic, as the preceding and following
        // WriteLine statements show. The type parameter names are
        // specified as an array of strings. To make the code
        // easier to read, each GenericTypeParameterBuilder is placed
        // in a variable with the same name as the type parameter.
        //
        string[] typeParamNames = {"TFirst", "TSecond"};
        GenericTypeParameterBuilder[] typeParams =
            myType.DefineGenericParameters(typeParamNames);

        GenericTypeParameterBuilder TFirst = typeParams[0];
        GenericTypeParameterBuilder TSecond = typeParams[1];

        Console.WriteLine("Type 'Sample' is generic: {0}",
            myType.IsGenericType);

        // Apply constraints to the type parameters.
        //
        // A type that is substituted for the first parameter, TFirst,
        // must be a reference type and must have a parameterless
        // constructor.
        TFirst.SetGenericParameterAttributes(
            GenericParameterAttributes.DefaultConstructorConstraint |
            GenericParameterAttributes.ReferenceTypeConstraint);

        // A type that is substituted for the second type
        // parameter must implement IExampleA and IExampleB, and
        // inherit from the trivial test class ExampleBase. The
        // interface constraints are specified as an array
        // containing the interface types.
        TSecond.SetBaseTypeConstraint(baseType);
        Type[] interfaceTypes = {interfaceA, interfaceB};
        TSecond.SetInterfaceConstraints(interfaceTypes);

        // The following code adds a private field named ExampleField,
        // of type TFirst.
        FieldBuilder exField =
            myType.DefineField("ExampleField", TFirst,
                FieldAttributes.Private);

        // Define a static method that takes an array of TFirst and
        // returns a List<TFirst> containing all the elements of
        // the array. To define this method it is necessary to create
        // the type List<TFirst> by calling MakeGenericType on the
        // generic type definition, List<T>. (The T is omitted with
        // the typeof operator when you get the generic type
        // definition.) The parameter type is created by using the
        // MakeArrayType method.
        //
        Type listOf = typeof(List<>);
        Type listOfTFirst = listOf.MakeGenericType(TFirst);
        Type[] mParamTypes = {TFirst.MakeArrayType()};

        MethodBuilder exMethod =
            myType.DefineMethod("ExampleMethod",
                MethodAttributes.Public | MethodAttributes.Static,
                listOfTFirst,
                mParamTypes);

        // Emit the method body.
        // The method body consists of just three opcodes, to load
        // the input array onto the execution stack, to call the
        // List<TFirst> constructor that takes IEnumerable<TFirst>,
        // which does all the work of putting the input elements into
        // the list, and to return, leaving the list on the stack. The
        // hard work is getting the constructor.
        //
        // The GetConstructor method is not supported on a
        // GenericTypeParameterBuilder, so it is not possible to get
        // the constructor of List<TFirst> directly. There are two
        // steps, first getting the constructor of List<T> and then
        // calling a method that converts it to the corresponding
        // constructor of List<TFirst>.
        //
        // The constructor needed here is the one that takes an
        // IEnumerable<T>. Note, however, that this is not the
        // generic type definition of IEnumerable<T>; instead, the
        // T from List<T> must be substituted for the T of
        // IEnumerable<T>. (This seems confusing only because both
        // types have type parameters named T. That is why this example
        // uses the somewhat silly names TFirst and TSecond.) To get
        // the type of the constructor argument, take the generic
        // type definition IEnumerable<T> (expressed as
        // IEnumerable<> when you use the typeof operator) and
        // call MakeGenericType with the first generic type parameter
        // of List<T>. The constructor argument list must be passed
        // as an array, with just one argument in this case.
        //
        // Now it is possible to get the constructor of List<T>,
        // using GetConstructor on the generic type definition. To get
        // the constructor of List<TFirst>, pass List<TFirst> and
        // the constructor from List<T> to the static
        // TypeBuilder.GetConstructor method.
        //
        ILGenerator ilgen = exMethod.GetILGenerator();

        Type ienumOf = typeof(IEnumerable<>);
        Type TfromListOf = listOf.GetGenericArguments()[0];
        Type ienumOfT = ienumOf.MakeGenericType(TfromListOf);
        Type[] ctorArgs = {ienumOfT};

        ConstructorInfo ctorPrep = listOf.GetConstructor(ctorArgs);
        ConstructorInfo ctor =
            TypeBuilder.GetConstructor(listOfTFirst, ctorPrep);

        ilgen.Emit(OpCodes.Ldarg_0);
        ilgen.Emit(OpCodes.Newobj, ctor);
        ilgen.Emit(OpCodes.Ret);

        // Create the type and save the assembly.
        Type finished = myType.CreateType();
        myAssembly.Save(myAsmName.Name+".dll");

        // Invoke the method.
        // ExampleMethod is not generic, but the type it belongs to is
        // generic, so in order to get a MethodInfo that can be invoked
        // it is necessary to create a constructed type. The Example
        // class satisfies the constraints on TFirst, because it is a
        // reference type and has a default constructor. In order to
        // have a class that satisfies the constraints on TSecond,
        // this code example defines the ExampleDerived type. These
        // two types are passed to MakeGenericMethod to create the
        // constructed type.
        //
        Type[] typeArgs = {typeof(Example), typeof(ExampleDerived)};
        Type constructed = finished.MakeGenericType(typeArgs);
        MethodInfo mi = constructed.GetMethod("ExampleMethod");

        // Create an array of Example objects, as input to the generic
        // method. This array must be passed as the only element of an
        // array of arguments. The first argument of Invoke is
        // null, because ExampleMethod is static. Display the count
        // on the resulting List<Example>.
        //
        Example[] input = {new Example(), new Example()};
        object[] arguments = {input};

        List<Example> listX =
            (List<Example>) mi.Invoke(null, arguments);

        Console.WriteLine(
            "\nThere are {0} elements in the List<Example>.",
            listX.Count);

        DisplayGenericParameters(finished);
    }

    private static void DisplayGenericParameters(Type t)
    {
        if (!t.IsGenericType)
        {
            Console.WriteLine("Type '{0}' is not generic.");
            return;
        }
        if (!t.IsGenericTypeDefinition)
        {
            t = t.GetGenericTypeDefinition();
        }

        Type[] typeParameters = t.GetGenericArguments();
        Console.WriteLine("\nListing {0} type parameters for type '{1}'.",
            typeParameters.Length, t);

        foreach( Type tParam in typeParameters )
        {
            Console.WriteLine("\r\nType parameter {0}:", tParam.ToString());

            foreach( Type c in tParam.GetGenericParameterConstraints() )
            {
                if (c.IsInterface)
                {
                    Console.WriteLine("    Interface constraint: {0}", c);
                }
                else
                {
                    Console.WriteLine("    Base type constraint: {0}", c);
                }
            }

            ListConstraintAttributes(tParam);
        }
    }

    // List the constraint flags. The GenericParameterAttributes
    // enumeration contains two sets of attributes, variance and
    // constraints. For this example, only constraints are used.
    //
    private static void ListConstraintAttributes(Type t)
    {
        // Mask off the constraint flags.
        GenericParameterAttributes constraints =
            t.GenericParameterAttributes & GenericParameterAttributes.SpecialConstraintMask;

        if ((constraints & GenericParameterAttributes.ReferenceTypeConstraint)
            != GenericParameterAttributes.None)
        {
            Console.WriteLine("    ReferenceTypeConstraint");
        }

        if ((constraints & GenericParameterAttributes.NotNullableValueTypeConstraint)
            != GenericParameterAttributes.None)
        {
            Console.WriteLine("    NotNullableValueTypeConstraint");
        }

        if ((constraints & GenericParameterAttributes.DefaultConstructorConstraint)
            !=GenericParameterAttributes.None)
        {
            Console.WriteLine("    DefaultConstructorConstraint");
        }
    }
}

/* This code example produces the following output:

Type 'Sample' is generic: False
Type 'Sample' is generic: True

There are 2 elements in the List<Example>.

Listing 2 type parameters for type 'Sample[TFirst,TSecond]'.

Type parameter TFirst:
    ReferenceTypeConstraint
    DefaultConstructorConstraint

Type parameter TSecond:
    Interface constraint: IExampleA
    Interface constraint: IExampleB
    Base type constraint: ExampleBase
 */
Imports System.Reflection
Imports System.Reflection.Emit
Imports System.Collections.Generic

' Define a trivial base class and two trivial interfaces 
' to use when demonstrating constraints.
'
Public Class ExampleBase
End Class

Public Interface IExampleA
End Interface

Public Interface IExampleB
End Interface

' Define a trivial type that can substitute for type parameter 
' TSecond.
'
Public Class ExampleDerived
    Inherits ExampleBase
    Implements IExampleA, IExampleB
End Class

Public Class Example
    Public Shared Sub Main()
        ' Define a dynamic assembly to contain the sample type. The
        ' assembly will not be run, but only saved to disk, so
        ' AssemblyBuilderAccess.Save is specified.
        '
        Dim myDomain As AppDomain = AppDomain.CurrentDomain
        Dim myAsmName As New AssemblyName("GenericEmitExample1")
        Dim myAssembly As AssemblyBuilder = myDomain.DefineDynamicAssembly( _
            myAsmName, _
            AssemblyBuilderAccess.RunAndSave)

        ' An assembly is made up of executable modules. For a single-
        ' module assembly, the module name and file name are the same 
        ' as the assembly name. 
        '
        Dim myModule As ModuleBuilder = myAssembly.DefineDynamicModule( _
            myAsmName.Name, _
            myAsmName.Name & ".dll")

        ' Get type objects for the base class trivial interfaces to
        ' be used as constraints.
        '
        Dim baseType As Type = GetType(ExampleBase)
        Dim interfaceA As Type = GetType(IExampleA)
        Dim interfaceB As Type = GetType(IExampleB)

        ' Define the sample type.
        '
        Dim myType As TypeBuilder = myModule.DefineType( _
            "Sample", _
            TypeAttributes.Public)

        Console.WriteLine("Type 'Sample' is generic: {0}", _
            myType.IsGenericType)

        ' Define type parameters for the type. Until you do this, 
        ' the type is not generic, as the preceding and following 
        ' WriteLine statements show. The type parameter names are
        ' specified as an array of strings. To make the code
        ' easier to read, each GenericTypeParameterBuilder is placed
        ' in a variable with the same name as the type parameter.
        ' 
        Dim typeParamNames() As String = {"TFirst", "TSecond"}
        Dim typeParams() As GenericTypeParameterBuilder = _
            myType.DefineGenericParameters(typeParamNames)

        Dim TFirst As GenericTypeParameterBuilder = typeParams(0)
        Dim TSecond As GenericTypeParameterBuilder = typeParams(1)

        Console.WriteLine("Type 'Sample' is generic: {0}", _
            myType.IsGenericType)

        ' Apply constraints to the type parameters.
        '
        ' A type that is substituted for the first parameter, TFirst,
        ' must be a reference type and must have a parameterless
        ' constructor.
        TFirst.SetGenericParameterAttributes( _
            GenericParameterAttributes.DefaultConstructorConstraint _
            Or GenericParameterAttributes.ReferenceTypeConstraint)

        ' A type that is substituted for the second type
        ' parameter must implement IExampleA and IExampleB, and
        ' inherit from the trivial test class ExampleBase. The
        ' interface constraints are specified as an array 
        ' containing the interface types.
        TSecond.SetBaseTypeConstraint(baseType)
        Dim interfaceTypes() As Type = {interfaceA, interfaceB}
        TSecond.SetInterfaceConstraints(interfaceTypes)

        ' The following code adds a private field named ExampleField,
        ' of type TFirst.
        Dim exField As FieldBuilder = _
            myType.DefineField("ExampleField", TFirst, _
                FieldAttributes.Private)

        ' Define a Shared method that takes an array of TFirst and 
        ' returns a List(Of TFirst) containing all the elements of 
        ' the array. To define this method it is necessary to create
        ' the type List(Of TFirst) by calling MakeGenericType on the
        ' generic type definition, List(Of T). (The T is omitted with
        ' the GetType operator when you get the generic type 
        ' definition.) The parameter type is created by using the
        ' MakeArrayType method. 
        '
        Dim listOf As Type = GetType(List(Of ))
        Dim listOfTFirst As Type = listOf.MakeGenericType(TFirst)
        Dim mParamTypes() As Type = {TFirst.MakeArrayType()}

        Dim exMethod As MethodBuilder = _
            myType.DefineMethod("ExampleMethod", _
                MethodAttributes.Public Or MethodAttributes.Static, _
                listOfTFirst, _
                mParamTypes)

        ' Emit the method body. 
        ' The method body consists of just three opcodes, to load 
        ' the input array onto the execution stack, to call the 
        ' List(Of TFirst) constructor that takes IEnumerable(Of TFirst),
        ' which does all the work of putting the input elements into
        ' the list, and to return, leaving the list on the stack. The
        ' hard work is getting the constructor.
        ' 
        ' The GetConstructor method is not supported on a 
        ' GenericTypeParameterBuilder, so it is not possible to get 
        ' the constructor of List(Of TFirst) directly. There are two
        ' steps, first getting the constructor of List(Of T) and then
        ' calling a method that converts it to the corresponding 
        ' constructor of List(Of TFirst).
        '
        ' The constructor needed here is the one that takes an
        ' IEnumerable(Of T). Note, however, that this is not the 
        ' generic type definition of IEnumerable(Of T); instead, the
        ' T from List(Of T) must be substituted for the T of 
        ' IEnumerable(Of T). (This seems confusing only because both
        ' types have type parameters named T. That is why this example
        ' uses the somewhat silly names TFirst and TSecond.) To get
        ' the type of the constructor argument, take the generic
        ' type definition IEnumerable(Of T) (expressed as 
        ' IEnumerable(Of ) when you use the GetType operator) and 
        ' call MakeGenericType with the first generic type parameter
        ' of List(Of T). The constructor argument list must be passed
        ' as an array, with just one argument in this case.
        ' 
        ' Now it is possible to get the constructor of List(Of T),
        ' using GetConstructor on the generic type definition. To get
        ' the constructor of List(Of TFirst), pass List(Of TFirst) and
        ' the constructor from List(Of T) to the static
        ' TypeBuilder.GetConstructor method.
        '
        Dim ilgen As ILGenerator = exMethod.GetILGenerator()

        Dim ienumOf As Type = GetType(IEnumerable(Of ))
        Dim listOfTParams() As Type = listOf.GetGenericArguments()
        Dim TfromListOf As Type = listOfTParams(0)
        Dim ienumOfT As Type = ienumOf.MakeGenericType(TfromListOf)
        Dim ctorArgs() As Type = {ienumOfT}

        Dim ctorPrep As ConstructorInfo = _
            listOf.GetConstructor(ctorArgs)
        Dim ctor As ConstructorInfo = _
            TypeBuilder.GetConstructor(listOfTFirst, ctorPrep)

        ilgen.Emit(OpCodes.Ldarg_0)
        ilgen.Emit(OpCodes.Newobj, ctor)
        ilgen.Emit(OpCodes.Ret)

        ' Create the type and save the assembly. 
        Dim finished As Type = myType.CreateType()
        myAssembly.Save(myAsmName.Name & ".dll")

        ' Invoke the method.
        ' ExampleMethod is not generic, but the type it belongs to is
        ' generic, so in order to get a MethodInfo that can be invoked
        ' it is necessary to create a constructed type. The Example 
        ' class satisfies the constraints on TFirst, because it is a 
        ' reference type and has a default constructor. In order to
        ' have a class that satisfies the constraints on TSecond, 
        ' this code example defines the ExampleDerived type. These
        ' two types are passed to MakeGenericMethod to create the
        ' constructed type.
        '
        Dim typeArgs() As Type = _
            {GetType(Example), GetType(ExampleDerived)}
        Dim constructed As Type = finished.MakeGenericType(typeArgs)
        Dim mi As MethodInfo = constructed.GetMethod("ExampleMethod")

        ' Create an array of Example objects, as input to the generic
        ' method. This array must be passed as the only element of an 
        ' array of arguments. The first argument of Invoke is 
        ' Nothing, because ExampleMethod is Shared. Display the count
        ' on the resulting List(Of Example).
        ' 
        Dim input() As Example = {New Example(), New Example()}
        Dim arguments() As Object = {input}

        Dim listX As List(Of Example) = mi.Invoke(Nothing, arguments)

        Console.WriteLine(vbLf & _
            "There are {0} elements in the List(Of Example).", _
            listX.Count _
        )

        DisplayGenericParameters(finished)
    End Sub

    Private Shared Sub DisplayGenericParameters(ByVal t As Type)

        If Not t.IsGenericType Then
            Console.WriteLine("Type '{0}' is not generic.")
            Return
        End If
        If Not t.IsGenericTypeDefinition Then _
            t = t.GetGenericTypeDefinition()

        Dim typeParameters() As Type = t.GetGenericArguments()
        Console.WriteLine(vbCrLf & _
            "Listing {0} type parameters for type '{1}'.", _
            typeParameters.Length, t)

        For Each tParam As Type In typeParameters

            Console.WriteLine(vbCrLf & "Type parameter {0}:", _
                tParam.ToString())

            For Each c As Type In tParam.GetGenericParameterConstraints()
                If c.IsInterface Then
                    Console.WriteLine("    Interface constraint: {0}", c)
                Else
                    Console.WriteLine("    Base type constraint: {0}", c)
                End If
            Next

            ListConstraintAttributes(tParam)
        Next tParam
    End Sub

    ' List the constraint flags. The GenericParameterAttributes
    ' enumeration contains two sets of attributes, variance and
    ' constraints. For this example, only constraints are used.
    '
    Private Shared Sub ListConstraintAttributes(ByVal t As Type)

        ' Mask off the constraint flags. 
        Dim constraints As GenericParameterAttributes = _
            t.GenericParameterAttributes And _
            GenericParameterAttributes.SpecialConstraintMask

        If (constraints And GenericParameterAttributes.ReferenceTypeConstraint) _
                <> GenericParameterAttributes.None Then _
            Console.WriteLine("    ReferenceTypeConstraint")

        If (constraints And GenericParameterAttributes.NotNullableValueTypeConstraint) _
                <> GenericParameterAttributes.None Then _
            Console.WriteLine("    NotNullableValueTypeConstraint")

        If (constraints And GenericParameterAttributes.DefaultConstructorConstraint) _
                <> GenericParameterAttributes.None Then _
            Console.WriteLine("    DefaultConstructorConstraint")

    End Sub

End Class

' This code example produces the following output:
'
'Type 'Sample' is generic: False
'Type 'Sample' is generic: True
'
'There are 2 elements in the List(Of Example).
'
'Listing 2 type parameters for type 'Sample[TFirst,TSecond]'.
'
'Type parameter TFirst:
'    ReferenceTypeConstraint
'    DefaultConstructorConstraint
'
'Type parameter TSecond:
'    Interface constraint: IExampleA
'    Interface constraint: IExampleB
'    Base type constraint: ExampleBase

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