GenericTypeParameterBuilder::SetInterfaceConstraints Method (array<Type^>^)

 

Sets the interfaces a type must implement in order to be substituted for the type parameter.

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

public:
[ComVisibleAttribute(true)]
void SetInterfaceConstraints(
	... array<Type^>^ interfaceConstraints
)

Parameters

interfaceConstraints
Type: array<System::Type^>^

An array of Type objects that represent the interfaces a type must implement in order to be substituted for the type parameter.

Interface constraints cannot be retrieved using methods of the GenericTypeParameterBuilder class. Once you have created the generic type that contains the type parameter, you can use its Type object to reflect the type parameters and their constraints. To get the type parameters of a completed generic type, use the Type::GetGenericArguments method. For each type parameter, get the base type constraint and interface constraints by using the Type::GetGenericParameterConstraints method.

The following code example creates a generic type with two type parameters, the second of which has two interface constraints, and saves them in the assembly GenericEmitExample1.dll. You can use the Ildasm.exe (IL Disassembler) to view the generated types. For a more detailed explanation of the steps involved in defining a dynamic generic type, see How to: Define a Generic Type with Reflection Emit.

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
 */

.NET Framework
Available since 2.0
Silverlight
Available since 2.0
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