Is there a way to build a new type during Runtime?

Question

I am going to ask a question that might sound weird.

Is there a way to build a new class during Runtime? Or at least, add a new property to an existing class.

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Answer 1

This is not a weird question - in some cases it might be very useful. For instance I use this technique for performance tests sometimes:

public static Type[] DynamicTypes;

public void CreateObjects()
{
  var codeNamespace = new CodeNamespace( "DynamicClasses" );
  codeNamespace.Imports.Add( new CodeNamespaceImport( "System" ) );
  codeNamespace.Imports.Add( new CodeNamespaceImport( "System.ComponentModel" ) );

  for( var i = 0; i < 2000; i++ )
  {
    var classToCreate = new CodeTypeDeclaration( "DynamicClass_" + i )
    {
      TypeAttributes = TypeAttributes.Public
    };
    var codeConstructor1 = new CodeConstructor
    {
      Attributes = MemberAttributes.Public
    };
    classToCreate.Members.Add( codeConstructor1 );

    codeNamespace.Types.Add( classToCreate );
  }

  var codeCompileUnit = new CodeCompileUnit();
  codeCompileUnit.Namespaces.Add( codeNamespace );

  var compilerParameters = new CompilerParameters
  {
    GenerateInMemory = true,
    IncludeDebugInformation = true,
    TreatWarningsAsErrors = true,
    WarningLevel = 4
  };
  compilerParameters.ReferencedAssemblies.Add( "System.dll" );

  var compilerResults = new CSharpCodeProvider().CompileAssemblyFromDom( compilerParameters, codeCompileUnit );

  if( compilerResults == null )
  {
    throw new InvalidOperationException( "ClassCompiler did not return results." );
  }
  if( compilerResults.Errors.HasErrors )
  {
    var errors = string.Empty;
    foreach( CompilerError compilerError in compilerResults.Errors )
    {
      errors += compilerError.ErrorText + "\n";
    }
    Debug.Fail( errors );
    throw new InvalidOperationException( "Errors while compiling the dynamic classes:\n" + errors );
  }

  var dynamicAssembly = compilerResults.CompiledAssembly;
  DynamicTypes = dynamicAssembly.GetExportedTypes();
}