IsBoxed Class

Definition

Namespace:

System.Runtime.CompilerServices

Assembly:

System.Runtime.CompilerServices.VisualC.dll

Indicates that the modified reference type is a boxed value type. This class cannot be inherited.

public ref class IsBoxed abstract sealed

public static class IsBoxed

type IsBoxed = class

Public Class IsBoxed

Inheritance

Object

IsBoxed

Examples

The following example demonstrates how to emit an IsBoxed object into an assembly using reflection.

#using <mscorlib.dll>

using namespace System;
using namespace System::Reflection;
using namespace System::Reflection::Emit;
using namespace System::Runtime::CompilerServices;
using namespace System::Threading;


ref class CodeEmitter
{
private:
    AssemblyBuilder^ asmBuilder;
    String^ asmName;
    ModuleBuilder^ modBuilder;


    void prepareAssembly(String^ name){
        
        // Check the input.
        if(!name){
        
            throw gcnew ArgumentNullException("AssemblyName");
        }

        asmName = name;

        // Create an AssemblyName object and set the name.
        AssemblyName^ asmName = gcnew AssemblyName();

        asmName->Name = name;

        // Use the AppDomain class to create an AssemblyBuilder instance.

        AppDomain^ currentDomain = Thread::GetDomain();

        asmBuilder = currentDomain->DefineDynamicAssembly(asmName,AssemblyBuilderAccess::RunAndSave);

        // Create a dynamic module.
        modBuilder = asmBuilder->DefineDynamicModule(name);
    }


public:

    // Constructor.
    CodeEmitter(String ^ AssemblyName){

        prepareAssembly(AssemblyName);
    }

    // Create a new type.
    TypeBuilder^ CreateType(String^ name){
       
        // Check the input.
        if(!name){
        
            throw gcnew ArgumentNullException("AssemblyName");
        }

        return modBuilder->DefineType( name );
    }

    // Write the assembly.
    void WriteAssembly(MethodBuilder^ entryPoint){
    
        // Check the input.
        if(!entryPoint){
        
            throw gcnew ArgumentNullException("entryPoint");
        }

        asmBuilder->SetEntryPoint( entryPoint );
        asmBuilder->Save( asmName );
    }

};

void main()
{

    // Create a CodeEmitter to handle assembly creation.
    CodeEmitter ^ e = gcnew CodeEmitter("program.exe");

    // Create a new type.
    TypeBuilder^ mainClass = e->CreateType("MainClass");
    
    // Create a new method.
    MethodBuilder^ mBuilder = mainClass->DefineMethod("mainMethod", MethodAttributes::Static);

    // Create an ILGenerator and emit IL for 
    // a simple "Hello World." program.
    ILGenerator^ ilGen = mBuilder->GetILGenerator();

    ilGen->Emit(OpCodes::Ldstr, "Hello World");

    array<Type^>^mType = {String::typeid};

    MethodInfo^ writeMI = Console::typeid->GetMethod( "WriteLine", mType );

    ilGen->EmitCall(OpCodes::Call, writeMI, nullptr );

    ilGen->Emit( OpCodes::Ret );

    /////////////////////////////////////////////////
    /////////////////////////////////////////////////
    // Apply a required custom modifier
    // to a field.
    /////////////////////////////////////////////////
    /////////////////////////////////////////////////

    array<Type^>^fType = {IsBoxed::typeid};

    mainClass->DefineField("modifiedInteger", Type::GetType("System.Int32"), fType, nullptr, FieldAttributes::Private);

    // Create the type.
    mainClass->CreateType();

    // Write the assembly using a reference to 
    // the entry point.
    e->WriteAssembly(mBuilder);

    Console::WriteLine(L"Assembly created.");
}

Remarks

The Microsoft C++ compiler supports boxed value types directly in the language. Information about boxed value types is emitted into metadata as a custom modifier, where the modifier decorates a reference to the value type being boxed.

Compilers emit custom modifiers within metadata to change the way that the just-in-time (JIT) compiler handles values when the default behavior is not appropriate. When the JIT compiler encounters a custom modifier, it handles the value in the way that the modifier specifies. Compilers can apply custom modifiers to methods, parameters, and return values. The JIT compiler must respond to required modifiers but can ignore optional modifiers.

You can emit custom modifiers into metadata using one of the following techniques:

• Using methods in the TypeBuilder class such as DefineMethod, DefineField, DefineConstructor, and DefineProperty.

• Generating a Microsoft intermediate language (MSIL) instruction file that contains calls to modopt and modreq, and assembling the file with the Ilasm.exe (IL Assembler).

• Using the unmanaged reflection API.