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From: sakkinen@tukki.jyu.fi (Markku Sakkinen)
Newsgroups: comp.lang.c++
Subject: Re: Overloaded Function Ambiguity Resolution Problems
Message-ID: <1991Mar8.105837.15493@tukki.jyu.fi>
Date: 8 Mar 91 10:58:37 GMT
References: <1991Feb27.084909.5063@newcastle.ac.uk> <1991Feb27.204841.14690@world.std.com>
Reply-To: sakkinen@jytko.jyu.fi (Markku Sakkinen)
Organization: University of Jyvaskyla, Finland
Lines: 54

In article <1991Feb27.204841.14690@world.std.com> wmm@world.std.com (William M Miller) writes:
>Graham.Parrington@newcastle.ac.uk (Graham D. Parrington) writes:
>> class Base
>> {
>> public:
>>     Base(char *) { cout << "Base::Base(char *)\n"; }
>>     void func(char*) { cout << "Base::func(char *)\n"; }
>> };
>>
>> class Derived:public Base
>> {
>> public:
>>     void func(const Base&){ cout << "Derived::func(const Base&)\n"; }
>>
>> };
>>
>> main()
>> {
>>     Derived *d = new Derived();
>>
>>     d->func("hello");
>> }
>>
>> What should it output?
>
>The cfront output is correct, G++ is wrong.  See E&S section 13.1, page 310:
>"Two function declarations of the same name refer to the same function if
>they are in the same scope and have identical argument types (section 13).
>A function member of a derived class is NOT in the same scope as a function
>member of the same name in a base class."  In this example, d->func("hello")
>can only refer to Derived::func(const Base&), since Base::func(char*) is
>hidden in the scope of Derived.
>
>-- William M. Miller, Glockenspiel, Ltd.
>   wmm@world.std.com

The functions in the example have _not_ got identical argument types!
The problem seems to be that a new function declared in a derived
class hides _all_ functions with the same name in the base class,
no matter what the number and types of arguments.
If the constructor 'Base (char*)' were not there,
the invocation of 'func' would evidently cause a compiler diagnostic.

Current C++ has a lot of complicated and stupid visibility rules,
as if expressly designed to shoot programmers in the back;
this is one of them.

Markku Sakkinen
Department of Computer Science and Information Systems
University of Jyvaskyla (a's with umlauts)
PL 35
SF-40351 Jyvaskyla (umlauts again)
Finland
          SAKKINEN@FINJYU.bitnet (alternative network address)