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<h4 class="subsubsection"> 4.3.1.4 Interface and implementation inheritance </h4>
<p>From time to time there might be a need or want for using normal inheritance
together with <small>SCF</small>. In practice there are two times you want to do this;
interface deriving from another interface to add methods and deriving from an
implementation class to add new interfaces.
</p>
<p>In the first case where you want an interface to extend another, the declaration
of the interfaces is straight forward using normal C++ inheritance. However, to
make the implementation class aware of the base interfaces it should also expose
you need to use the <code>scfFakeInterface<></code> template class in the parameter
to <code>scfImplementationN<></code>.
</p>
<p>Example:
</p>
<table><tr><td> </td><td><pre class="example">// Abstract interface file (itest2.h)
struct iTestBase : public virtual iBase
{
SCF_INTERFACE (iTestBase, 1, 0, 0);
...
virtual void SomeFunction () = 0;
};
struct iTest2 : public iTestBase
{
SCF_INTERFACE (iTest2, 1, 0, 0);
...
virtual void NewFunction () = 0;
};
// Concrete implementation header (test2.h)
class Test2 : public scfImplementation2<Test2,
scfFakeInterface<iTestBase>,
iTest2>
{
...
};
</pre></td></tr></table>
<p>The other situation is when you want to take an already existing implementation
class, derive from it and add one or more new interfaces. Using only normal C++
inheritance and <code>scfImplementationN<></code> like above is the right way to go if
the base class does not implement any <small>SCF</small> interfaces, if they do you need
to use the extra functionality that the template <code>scfImplementationExtN<></code>.
</p>
<p><code>scfImplementationExtN<></code> have same template parameters as
<code>scfImplementationN<></code> with one difference, the second parameter is the base
class to use.
</p>
<p>Example: Lets extend Test2 from above with one more interface
</p>
<table><tr><td> </td><td><pre class="example">struct iNewIf : public virtual iBase
{
SCF_INTERFACE (iNewIf, 1, 0, 0);
virtual void PrintMe () = 0;
}
class NewTest2 : public scfImplementationExt1<NewTest2, Test2, iNewIf>
{
...
void PrintMe ();
}
</pre></td></tr></table>
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