Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!microsoft!jimad
From: jimad@microsoft.UUCP (Jim ADCOCK)
Newsgroups: comp.lang.c++
Subject: Re: Static initialization
Keywords: static initialize virtual
Message-ID: <72347@microsoft.UUCP>
Date: 14 May 91 19:41:15 GMT
References: <1991May10.063358.15955@ccu1.aukuni.ac.nz>
Reply-To: jimad@microsoft.UUCP (Jim ADCOCK)
Organization: Microsoft Corp., Redmond WA
Lines: 34

In article <1991May10.063358.15955@ccu1.aukuni.ac.nz> gkean@ccu1.aukuni.ac.nz (Graham Kean;;g_kean) writes:
|Can anyone tell me why it is not possible to statically
|initialize an instance of a class containing virtual functions?
|
|class TESTCLASS
|    {
|    public:
|	int a,b,c;
|	virtual void testfunc();
|    };
|void TESTCLASS::testfunc() {}
|TESTCLASS test = {1,2,3};

The problem is not that you are trying to statically initialize an
instance of a class containing virtual functions, but rather that
you are trying to initialize a class with virtual functions with
an initializer list.  ARM 8.4.1 states that you are only allowed
to use initializer lists with objects of classes with no constructors,
no private nor protected members, no bases classes, nor any virtual 
functions.  I don't see where there would be any great difficulty for
most compilers to statically initialize your vtable pointer, its
just that the standard tells them not to do so.

I'd guess the rationale is that if you want to be using inheritence
and polymophism, you really "ought" to be be doing it the C++ way,
using constructors to get your object to a safe default state,
and then use member functions to modify that state.  Alternatively,
for C backwards compatibility with C-like structures, C++ still
supports initializer lists.  Compilers could be required to support
strategies that fall in between, but I guess it wasn't considered
worthwhile.  With the present rules, compiler writers are assured that
all vtable ptr initializations can happen within compiler generated
constructors.  Your desired feature would require them to be a little
bit smarter.