Andrey Tarasevich
11/18/2008 10:35:00 PM
Marcel Müller wrote:
> In the code below gcc says
>
> test.cpp: In constructor `SingleInfoDialog::SingleInfoDialog(const
> PlayableSetBase&)':
> test.cpp:2: error: `class PlayableSetBase' is inaccessible
> test.cpp:24: error: within this context
>
> Obviosly gcc does not manage to pass the parameter of type const
> PlayableSetBase& to the constructor of InfoDialog because there is a
> private base class with the same name. Is this really not allowed?
There's not just a private base class with that name, but also the name
of that base class is implicitly introduced into the derived class'
scope (it is called "base class name injection"). Class
'PlayableSetBase' is a base class of class 'OwnedPlayableSet', which
means that 'PlayableSetBase' is injected into the 'OwnedPlayableSet'
scope, as if an invisible typedef declaration was there
class OwnedPlayableSet
: public PlayableSetBase
{ public:
...
typedef ::PlayableSetBase PlayableSetBase;
...
};
Now, whenever you use the unqualified 'PlayableSetBase' in any derived
class, it actually refers not to the file-scope name, but to that
class-scope name implicitly declared in 'OwnedPlayableSet'.
In your example, 'InfoDialog' inherits from 'OwnedPlayableSet'
privately, meaning that now 'PlayableSetBase' is private in
'InfoDialog'. And finally, you are trying to access the private
'PlayableSetBase' from 'SingleInfoDialog', which causes the error.
To fix the error, tell the compiler that you want to refer to the global
'PlayableSetBase' name, not the inherited private 'PlayableSetBase' name.
class SingleInfoDialog
: public InfoDialog
{public:
SingleInfoDialog(const ::PlayableSetBase& key)
: InfoDialog(key)
{}
};
>
> -----
> class PlayableSetBase
> {
> };
>
> class OwnedPlayableSet
> : public PlayableSetBase
> {public:
> OwnedPlayableSet(const PlayableSetBase& r);
> };
>
>
> class InfoDialog
> // a member is not sufficient because of the destruction sequence
> : private OwnedPlayableSet
> {protected:
> InfoDialog(const PlayableSetBase& key)
> : OwnedPlayableSet(key)
> {}
> };
>
> class SingleInfoDialog
> : public InfoDialog
> {public:
> SingleInfoDialog(const PlayableSetBase& key)
> : InfoDialog(key) // <-- !!!
> {}
> };
--
Best regards,
Andrey Tarasevich