Guide pratique pour définir un type générique avec l’émission de réflexion

Article
04/05/2024

Cet article explique comment créer un type générique simple avec deux paramètres de type, comment appliquer des contraintes de classe, des contraintes d’interface et des contraintes spéciales aux paramètres de type, et comment créer des membres qui utilisent les paramètres de type de la classe comme types de paramètres et types de retour.

Important

Une méthode n’est pas générique simplement car elle appartient à un type générique et utilise les paramètres de type de ce type. Une méthode est générique uniquement si elle a sa propre liste de paramètres de type. La plupart des méthodes sur les types génériques ne sont pas génériques, comme dans cet exemple. Pour obtenir un exemple d’émission de méthode générique, consultez Guide pratique pour définir une méthode générique avec l’émission de réflexion.

Définir un type générique

Définissez un assembly dynamique nommé GenericEmitExample1. Dans cet exemple, l’assembly est exécuté et enregistré sur le disque. AssemblyBuilderAccess.RunAndSave est donc spécifié.

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)

Définissez un module dynamique. Un assembly est composé de modules exécutables. Pour un assembly à module unique, le nom du module est identique au nom de l’assembly, et le nom de fichier est le nom du module suivi d’une extension.

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")

Définissez une classe. Dans cet exemple, la classe se nomme 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)

Définissez les paramètres de type générique de Sample en passant un tableau de chaînes contenant les noms des paramètres à la méthode TypeBuilder.DefineGenericParameters. Cela fait de la classe un type générique. La valeur de retour est un tableau d’objets GenericTypeParameterBuilder représentant les paramètres de type, qui peut être utilisé dans votre code émis.

Dans le code suivant, Sample devient un type générique avec les paramètres de type TFirst et TSecond. Pour faciliter la lecture du code, chaque GenericTypeParameterBuilder est placé dans une variable du même nom que le paramètre de type.

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)

Ajoutez des contraintes spéciales aux paramètres de type. Dans cet exemple, le paramètre de type TFirst est limité aux types qui ont des constructeurs sans paramètre et aux types référence.

TFirst->SetGenericParameterAttributes( 
    GenericParameterAttributes::DefaultConstructorConstraint | 
    GenericParameterAttributes::ReferenceTypeConstraint 
);

TFirst.SetGenericParameterAttributes(
    GenericParameterAttributes.DefaultConstructorConstraint |
    GenericParameterAttributes.ReferenceTypeConstraint);

TFirst.SetGenericParameterAttributes( _
    GenericParameterAttributes.DefaultConstructorConstraint _
    Or GenericParameterAttributes.ReferenceTypeConstraint)

Ajoutez éventuellement des contraintes de classe et d’interface aux paramètres de type. Dans cet exemple, le paramètre de type TFirst est limité aux types qui dérivent de la classe de base représentée par l’objet Type contenu dans la variable baseType, et qui implémentent les interfaces dont les types sont contenus dans les variables interfaceA et interfaceB. Pour plus d’informations sur la déclaration et l’assignation de ces variables, consultez l’exemple de code.
```
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)
```

Définissez un champ. Dans cet exemple, le type du champ est spécifié par le paramètre de type TFirst. GenericTypeParameterBuilder dérive de Type. Vous pouvez donc utiliser des paramètres de type générique partout où un type peut être utilisé.

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)

Définissez une méthode qui utilise les paramètres de type du type générique. Notez que ces méthodes ne sont génériques que si elles ont leurs propres listes de paramètres de type. Le code suivant définit une méthode static (Shared en Visual Basic) qui prend un tableau de TFirst et retourne un List<TFirst> (List(Of TFirst) en Visual Basic) contenant tous les éléments du tableau. Pour définir cette méthode, vous devez créer le type List<TFirst> en appelant MakeGenericType sur la définition de type générique, List<T>. (Le T est omis quand vous utilisez l’opérateur typeof (GetType en Visual Basic) pour obtenir la définition de type générique.) Le type de paramètre est créé à l’aide de la méthode MakeArrayType.

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)

Émettez le corps de méthode. Le corps de la méthode se compose de trois opcodes qui chargent le tableau d’entrée sur la pile, appellent le constructeur List<TFirst> qui accepte IEnumerable<TFirst> (qui fait tout le travail nécessaire pour placer les éléments d’entrée dans la liste), et retournent (en laissant le nouvel objet List<T> sur la pile). La partie difficile de l’émission de ce code consiste à obtenir le constructeur.

La méthode GetConstructor n’étant pas prise en charge sur un GenericTypeParameterBuilder, vous ne pouvez pas obtenir directement le constructeur de List<TFirst>. Vous devez d’abord obtenir le constructeur de la définition de type générique List<T>, puis appeler une méthode qui le convertit en constructeur de List<TFirst> correspondant.

Le constructeur utilisé pour cet exemple de code prend un IEnumerable<T>. Notez cependant qu’il ne s’agit pas de la définition de type générique de l’interface générique IEnumerable<T>. Au lieu de cela, le paramètre de type T de List<T> doit remplacer le paramètre de type T de IEnumerable<T>. (Cela semble déroutant uniquement parce que les deux types ont des paramètres de type nommés T. C’est pourquoi cet exemple de code utilise les noms TFirst et TSecond.) Pour obtenir le type de l’argument constructeur, commencez par la définition IEnumerable<T> de type générique et appelez MakeGenericType avec le premier paramètre de type générique List<T>. La liste d’arguments de constructeur doit être passée en tant que tableau, avec un seul argument dans ce cas.

Notes

La définition de type générique est exprimée en tant que IEnumerable<> quand vous utilisez l’opérateur typeof en C#, ou IEnumerable(Of ) quand vous utilisez l’opérateur GetType en Visual Basic.

Il est désormais possible d’obtenir le constructeur de List<T> en appelant GetConstructor sur la définition de type générique. Pour convertir ce constructeur en constructeur correspondant de List<TFirst>, transmettez List<TFirst> et le constructeur de List<T> à la méthode statique TypeBuilder.GetConstructor(Type, ConstructorInfo).
```
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)
```

Créez le type et enregistrez le fichier.

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")

Appelez la méthode. ExampleMethod n’est pas générique, mais le type auquel il appartient est générique. Ainsi, pour obtenir un MethodInfo qui peut être appelé, il est nécessaire de créer un type construit à partir de la définition de type de Sample. Le type construit utilise la classe Example, ce qui satisfait aux contraintes sur TFirst car il s’agit d’un type référence avec un constructeur sans paramètre par défaut, et la classe ExampleDerived qui satisfait aux contraintes sur TSecond. (Le code de ExampleDerived se trouve dans la section Exemple de code.) Ces deux types sont passés à MakeGenericType pour créer le type construit. MethodInfo est ensuite obtenu à l’aide de la méthode GetMethod.
```
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")
```

Le code suivant crée un tableau d’objets Example, place ce tableau dans un tableau de type Object représentant les arguments de la méthode à appeler, puis les passe à la méthode Invoke(Object, Object[]). Le premier argument de la méthode Invoke est une référence null car la méthode est 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 _
)

Exemple

L’exemple de code suivant définit une classe nommée Sample, ainsi qu’une classe de base et deux interfaces. Le programme définit deux paramètres de type générique pour Sample, ce qui en fait un type générique. Les paramètres de type sont la seule chose qui rend un type générique. Le programme l’indique en affichant un message de test avant et après la définition des paramètres de type.

Le paramètre de type TSecond sert à illustrer les contraintes de classe et d’interface, à l’aide des interfaces et de la classe de base, et le paramètre de type TFirst sert à illustrer des contraintes spéciales.

L’exemple de code définit un champ et une méthode à l’aide des paramètres de type de la classe pour le type de champ et pour le paramètre et le type de retour de la méthode.

Une fois la classe Sample créée, la méthode est appelée.

Le programme inclut une méthode qui répertorie les informations sur un type générique, et une méthode qui répertorie les contraintes spéciales sur un paramètre de type. Ces méthodes sont utilisées pour afficher des informations sur la classe Sample finie.

Le programme enregistre le module fini sur le disque en tant que GenericEmitExample1.dll. Ainsi, vous pouvez l’ouvrir avec Ildasm.exe (désassembleur IL) et examiner le code CIL de la classe Sample.

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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Guide pratique pour définir un type générique avec l’émission de réflexion

Définir un type générique

Exemple

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Ressources supplémentaires