mneerach@c.inf.ethz.ch (Matthias Ulrich Neeracher) (08/30/90)
Recently, I tried to use a protected base class, like this:
class A {
...
};
class B:protected A {
...
};
To my surprise, my compiler (based on CFront 2.0) refused to compile this.
The ARM doesn't seem to be clear about this: The syntax seems to allow it,
but the text and examples don't mention it.
My question is: If protected base classes are indeed illegal, why are they
and what speaks against adding them to C++ ?
I hope this question is not inappropriate for this newsgroup.
Matthias
-----
Matthias Neeracher mneerach@inf.ethz.ch
"I wouldn't recommend sex, drugs or insanity for everyone,
but they've always worked for me" -- Hunter S. Thompsonbs@alice.UUCP (Bjarne Stroustrup) (08/31/90)
The summaries say it all.
hansen@pegasus.ATT.COM (Tony L. Hansen) (09/01/90)
< Recently, I tried to use a protected base class, like this:
< class A { ... };
< class B: protected A { ... };
< To my surprise, my compiler (based on CFront 2.0) refused to compile this.
< The ARM doesn't seem to be clear about this: The syntax seems to allow it,
< but the text and examples don't mention it.
< My question is: If protected base classes are indeed illegal, why are they
< and what speaks against adding them to C++ ?
The introduction of protected base classes occurred this year as part of the
1990 C++ definition. The AT&T 2.1 C++ Reference Manual, and subsequently The
Annotated C++ Reference Manual (E&S), documents its introduction.
However, NO compiler currently implements protected base classes, not even
AT&T's 2.1. Also, the exact semantics have NOT been cast in stone, although
it's unlikely that they will differ much from the following description:
The visibility of the members of a base class are "capped" at the level of
the access specifier given for the base class. For the following example:
class base
{
public: int bpublic;
private: int bprivate;
protected:int bprotected;
};
class derived : class derived : class derived :
public base protected base private base
{ { {
... ... ...
}; }; };
the visibility of the different base members are adjusted as follows for the
various members of base using the different access specifications:
access spec: public protected private
----------------------------------------------------------------
bpublic: public protected private
bprotected: protected protected private
bprivate: not accessible not accessible not accessible
I hope this helps.
< I hope this question is not inappropriate for this newsgroup.
I'd say it's perfectly appropriate for this newsgroup.
Tony Hansen
att!pegasus!hansen, attmail!tony
hansen@pegasus.att.comjimad@microsoft.UUCP (Jim ADCOCK) (09/05/90)
In article <5026@neptune.inf.ethz.ch> mneerach@c.inf.ethz.ch (Matthias Ulrich Neeracher) writes: > >class B:protected A { > ... >}; > >To my surprise, my compiler (based on CFront 2.0) refused to compile this. >The ARM doesn't seem to be clear about this: The syntax seems to allow it, >but the text and examples don't mention it. Existing compilers are not reliable indicators of the fine-grained details of the standardization effort. E&S is. Compilers claiming "2.1" compatibility may be pretty close to E&S. >My question is: If protected base classes are indeed illegal, why are they >and what speaks against adding them to C++ ? My understanding is that protected base classes will be allowed. Unfortunately, I cannot find the appropriate reference in E&S. [Though I'm sure I read it somewhere....]