Hi,
I am new to .Net, ADO.Net and i have to programm an independent dataprovider
(no sql, no oledb, no odbc) and in addition it has to be in visual c++
untill now i have two classes.
Class Conn derived from IDbConnection and class comm derived from idbcommand.

so my problem is the method 'Comm* CreateCommand' in class Conn, i allways
get the error message error C2392: ..... : Covariant-Returntype
WTF is that?????


__gc class Comm;
__gc class Conn : public IDbConnection
{
......
Comm* CreateCommand(){Comm* cmd = new Comm();
cmd->set_Connection(this);
return cmd;};
IDbCommand* IDbConnection::CreateCommand(){return this::CreateCommand();};
......
}


__gc class Comm : public IDbCommand
{
.......
}

My guess is that compiler generate the same signature for "Comm
*CreateCommand" method and "IDbConnection *CreateCommand". Probably because
Comm inherit from IDbConnection.
I don't understand why you need to have two public methods. May be you can
just rename "Comm *CreateCommand" method to "_CreateCommand".

Just one advice, I experienced the same project: I had to program a data
provider for a legacy data source. I'd choose to have two layers:
- a C++ managed layer in a DLL to call legacy data source
- a C# assembly to implement the ADO.NET provider interface and call my C++
layer.

I think it's simpler than mixed legacy call and ADO.NET interface.

Lionel.

"Peter" <(E-Mail Removed)> a écrit dans le message de news:
2E83D61E-A5EB-4F74-8A4D-(E-Mail Removed)...
> Hi,
> I am new to .Net, ADO.Net and i have to programm an independent
> dataprovider
> (no sql, no oledb, no odbc) and in addition it has to be in visual c++
> untill now i have two classes.
> Class Conn derived from IDbConnection and class comm derived from
> idbcommand.
>
> so my problem is the method 'Comm* CreateCommand' in class Conn, i allways
> get the error message error C2392: ..... : Covariant-Returntype
> WTF is that?????
>
>
> __gc class Comm;
> __gc class Conn : public IDbConnection
> {
> .....
> Comm* CreateCommand(){Comm* cmd = new Comm();
> cmd->set_Connection(this);
> return cmd;};
> IDbCommand* IDbConnection::CreateCommand(){return this::CreateCommand();};
> .....
> }
>
>
> __gc class Comm : public IDbCommand
> {
> ......
> }