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methodscomatlchainingidl

Chaining methods of ATL/COM objects

In c++ we can easily set up method chaining in a class by designing methods returning *this. Would this be possible in an ATL/COM setting ? Let's say I have a simple ATL class MyOBj. I would like to know if chaining is possible in this context, and if so, what would be the idl signature of the method that would support chaining ? Simple examples would be appreciated ! (In fact, my methods are called from VBA for excel, and I would like to have chaining in that VBA context, as we have chaining already for standard VBA methods.)

Thx a lot

R

EDIT :

In the .idl file I have this :

interface IRateModel : IDispatch{
    [id(1), helpstring("SETRATEMODEL")] HRESULT SETRATEMODEL( [in] VARIANT * var_in ) ;
    [id(2), helpstring("GETRATETERMSTRUCTURE")] HRESULT GETRATETERMSTRUCTURE( [in, out] VARIANT * var_in ) ;
};

interface IVolatilityModel : IDispatch{
    [id(1), helpstring("SETVOLATILITYMODEL")] HRESULT SETVOLATILITYMODEL( [in] VARIANT * var_in ) ;
    [id(2), helpstring("GETVOLATILITY")] HRESULT GETVOLATILITY( [in, out] VARIANT * var_in ) ;
};

interface IMyOption : IDispatch{
    [id(1), helpstring("SETMATURITY")] HRESULT SETMATURITY( [in] VARIANT * TheMaturity, [out,retval] IMyOption ** ret ) ;
    [id(2), helpstring("SETSTRIKE")] HRESULT SETSTRIKE( [in] VARIANT * TheStrike, [out,retval] IMyOption ** ret ) ;
    [id(3), helpstring("SETPAYOFF")] HRESULT SETPAYOFF( [in] VARIANT * ThePayoff, [out,retval] IMyOption ** ret ) ;
    [id(4), helpstring("ATTACHRATEMODEL")] HRESULT ATTACHRATEMODEL( [in] IRateModel ** TheRateModel, [out,retval] IMyOption ** ret ) ;
    [id(5), helpstring("ATTACHVOLATILITYPROCESS")] HRESULT ATTACHVOLATILITYPROCESS( [in] IVolatilityModel ** TheVolatilityModel, [out,retval] IMyOption ** ret ) ;
    [id(6), helpstring("PRICEIT")] HRESULT PRICEIT( [in, out] DOUBLE * price ) ;
};

SETRATEMODEL's implementation is :

STDMETHODIMP CRateModel::SETRATEMODEL( /*[in]*/ VARIANT * var_in )
{
    // something
    // ...

    return S_OK ;
}

This implementation hasn't changed since I added other interface. Before adding them, at debug, the VARIANT was as VT_R8 (coming from a vba VARIANT, this one coming from an excel's double) Now at debug, the variant is a VT_DISPATCH.

PS : I'm a very fresh-starter in ATL/COM.

Solution

  • Something like this:

    interface IMyInterface {
  HRESULT DoSomething([in] long someParam, [out, retval] IMyInterface** ret);
  HRESULT DoSomethingElse([out, retval] IMyInterface** ret);
};

    Scripting clients should be able to do myObj.DoSomething(42).DoSomethingElse()