Re: private inheritance and ambiguous base
On Feb 24, 10:26 am, James Kanze <james.ka...@gmail.com> wrote:
On Feb 23, 10:03 pm, Victor Bazarov <v.baza...@comcast.invalid> wrote:
On 2/23/2011 4:49 PM, nguillot wrote:
Here an example of is-implemented-in-term-of (or has-a) relation, wit=
h
a private inheritance:
(please, this is sample code to illustrate my question, don't suggest
me to use composition, even if you would be right).
every class that wants to log must inherit from the following class:
class Loggable
{
protected:
Loggable(std::string className) : className_(className) {}
void Log(std::string text)
{
// a log function, for instance:
std::cout<< className_<< ": "<< text<< =
endl;
}
private:
std::string className_;
};
Let's have a class A that wants to log:
class A : private Loggable
{
public:
A() : Loggable("A")
{
Log("blabla");
}
};
So far, so good
Now, let's have a class B that wants to log, and inherits from A:
class B : private Loggable, public A
{
public:
B() : Loggable("B")
{
Log("blbblb");
}
};
It produces a warning:
warning: direct base Loggable inaccessible in B due to ambiguity
and an error:
error: reference to Log is ambiguous
error: candidates are: void Loggable::Log(std::string)
error: void Loggable::Log(std::string=
)
A solution would to use virtual inheritance from Loggable, but I thin=
k
it's not what I want:
Maybe it's ambigous for the compiler which Loggable base to use when
we use Log in B, but it's not: as I use private inheritance, the
A::Log should'nt be available in B...
Access rights are not considered when names are resolved. Name
resolution is what causes ambiguity. You can solve name resolution i=
f
you provide a hint to the compiler:
B() : Loggable("B")
{
Loggable::Log("blbblb");
}
The whole point of the error message is that there is no way to
qualify Loggable in a way which specifies the direct base of B.
Loggable:: specifies the Loggable base of B, direct or indirect,
and is ambiguous. The only way to work around the problem is to
introduce an intermediate class, e.g.:
Is B::Loggable::Log( "afa" ) stadard?
itaj
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