Forward declaration with value class

[Jerome]

Hi all,

I'm trying to use forward declaration with value class but I don't succeed
in compiling my (quite simple) sample code.
This is my code I'm trying to compile (Visual Studio 2003)

namespace managedDll
{
public __value class VecDouble;
public __value class VecFloat
{
public:
void SetValue(VecDouble vec)

{
// TODO
}

};

public __value class VecDouble
{

public:
void SetValue(VecFloat vec)

{
// TODO
}

};
}

I've got the following error when compiling:
error C2027: use of undefined type 'managedDll::VecDouble'

Every think work fine if my SetValues methods have the signature (Vec(Double
| Float) &vec).
The problem is that putting a '&' is not logical because I want to call
methods from C# code and with this signature I should write the following
code

VecDouble vec = new VecDouble();
vecFloat.SetValue(ref vec);

Instead I want to call my methods in this way:
vecFloat.SetValue(new VecDouble())
The first solution is not acceptable !.

Does anyone encounter the same problem ?

Great thanks.
Jerome

 

[Eckart Haug]

Forward declaration by definition only works with pointers (VecDouble* vec) and refenences (VecDouble& vec).
This is because in this cases the parameter is just an address. If you pass an object by value, the compiler
creates a copy of the object on the stack - and therefore needs all the information of the object, e.g. how
many bytes it occupies, whether it has a copy constructor and so on.

 

[Jerome]

I know that ... and that's why I think there's a problem with managed C++
language.
It's not acceptable that a method you think taking a parameter as 'In' must
be signed by 'ref'
Of course the problem does not exists with reference class.

I'm still dreaming of a magic attribute or magic compilation option ... who
knows ? ... certainly Microsoft developpers ... Anyone from Microsoft Visual
Studio team to solve my issue or explain why it can't be possible ???

Forward declaration by definition only works with pointers (VecDouble*

vec) and refenences (VecDouble& vec).

This is because in this cases the parameter is just an address. If you

pass an object by value, the compiler

creates a copy of the object on the stack - and therefore needs all the

information of the object, e.g. how

 

[James Park]

How about something like this:
namespace managedDll
{
public __value class VecDouble;
public __value class VecFloat
{
public:
void SetValue(VecDouble vec);
};

public __value class VecDouble
{
public:
void SetValue(VecFloat vec)
{
// TODO
}
};

void VecFloat::SetValue(VecDouble vec)
{
// TODO
}
}

 

[Jerome]

It works !
I try so much things that I don't try the simple one ...

Great thanks !