C++ Windows Application Form Cannot make Forward Declaration

Question

I am using Visual C++ 2010, in Windows Application Form:

#pragma once

namespace MyProgram {

using namespace System;
using namespace System::IO;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Windows::Forms;
using namespace System::Data;
using namespace System::Drawing;

ref class Design;       //Forward Declariong of Class Design

/// <summary>
/// Summary for Form1
/// </summary>
public ref class Form1 : public System::Windows::Forms::Form
{
private:
    Design Enviroment;  //Declaring object of class: Design
public:
    Form1(void)
    {
        InitializeComponent();
        //
        //TODO: Add the constructor code here
        //
    }
    };


public ref class Design
    {
    private:
        String^ Color;
    public:
        Design()
                {
                     //TODO: Add the Constructor code here
                }
    };

And i get the error: MyProgram::Form1::Enviroment' uses undefined class 'MyProgram::Design'

If I switch the definition order, it will compile with no errors, but in windows application form the class Form1 always has to be first... So, is my forward declaration wrong?

Answer 1

Since you are declaring a variable (Environment) of type Design the complete type has to be available to the compiler at that time.

By re-ordering your declarations, you are providing the complete type to the compiler.