Re: Testing Program Question

From:

"Leigh Johnston" <leigh@i42.co.uk>

Newsgroups:

comp.lang.c++

Date:

Mon, 1 Mar 2010 13:33:08 -0000

Message-ID:

<ivudnbB6yuSDXxbWnZ2dnUVZ8kqdnZ2d@giganews.com>

Look at Microsoft's COM which is something which is employed with larger
code sizes. In C++ terms a COM interface is just like a Java interface
implemented as an abstract class containing just public pure virtual
functions and no implementation code and/or data. It is possible to wrap
such virtuals with a non-virtual function which can do parameter and/or
return value checking (arguably only required for debug builds) but it is
not possible to do an invariant check at the call site.

Not entirely true what I said but almost: take a look at the core COM
interface IUnknown below, note the public pure virtuals and the non-virtual
wrapper helper function (which must be inline and doesn't involve accessing
any state or any invariant check).

    extern "C++"
    {
        MIDL_INTERFACE("00000000-0000-0000-C000-000000000046")
        IUnknown
        {
        public:
            BEGIN_INTERFACE
            virtual HRESULT STDMETHODCALLTYPE QueryInterface(
                /* [in] */ REFIID riid,
                /* [iid_is][out] */ __RPC__deref_out void __RPC_FAR
*__RPC_FAR *ppvObject) = 0;

            virtual ULONG STDMETHODCALLTYPE AddRef( void) = 0;

            virtual ULONG STDMETHODCALLTYPE Release( void) = 0;

            template<class Q>
            HRESULT
#ifdef _M_CEE_PURE
            __clrcall
#else
            STDMETHODCALLTYPE
#endif
            QueryInterface(Q** pp)
            {
                return QueryInterface(__uuidof(Q), (void **)pp);
            }

            END_INTERFACE
        };
    } // extern C++