c++/7181: foo<n>::bar = foo<n-1>::bar + foo<n-2>::bar evaluates to zero at compile time

[Mark Mitchell]

The following reply was made to PR c++/7181; it has been noted by GNATS.

From: Mark Mitchell <mark@codesourcery.com>
To: Nathan Sidwell <nathan@codesourcery.com>,
   "mmitchel@gcc.gnu.org" <mmitchel@gcc.gnu.org>,
   "dobrynin@bigfoot.com" <dobrynin@bigfoot.com>,
   "gcc-bugs@gcc.gnu.org" <gcc-bugs@gcc.gnu.org>,
   "gcc-prs@gcc.gnu.org" <gcc-prs@gcc.gnu.org>,
   "nobody@gcc.gnu.org" <nobody@gcc.gnu.org>,
   "gcc-gnats@gcc.gnu.org" <gcc-gnats@gcc.gnu.org>
Cc:  
Subject: Re: c++/7181: foo<n>::bar = foo<n-1>::bar + foo<n-2>::bar evaluates
 to  zero at compile time
Date: Tue, 02 Jul 2002 13:08:21 -0700

 --On Tuesday, July 02, 2002 08:42:23 PM +0100 Nathan Sidwell 
 <nathan@codesourcery.com> wrote:
 
 > mmitchel@gcc.gnu.org wrote:
 >>
 >> Synopsis: foo<n>::bar = foo<n-1>::bar + foo<n-2>::bar evaluates to zero
 >> at compile time
 >>
 >> State-Changed-From-To: analyzed->closed
 >> State-Changed-By: mmitchel
 >> State-Changed-When: Tue Jul  2 11:31:51 2002
 >> State-Changed-Why:
 >>     This code does not have well-defined behavior.
 > How have you come to this conclusion? The last sentance of
 > [14.7.1]/1 indicates that we must instantiate the definition of
 > Foo<N>::value. I see nothing in [3.6.2] or [3.8] which disallows it.
 >
 > Or are you saying this is a case of [14.7.3]/7?\
 
 The standard doesn't specifies that the point of instantiation for the
 various static data members is "the same".  It doesn't say which one
 gets instantiated first.  Nor, according to John, does it say which one
 gets initialized first.
 
 So, I think the standard says "all those things get instantiated and
 initialized in some order" -- but not which order, similar to the
 example in 3.6.2.
 
 These are dynamic initializations; the initializers are not constant
 expressions.
 
 -- 
 Mark Mitchell                mark@codesourcery.com
 CodeSourcery, LLC            http://www.codesourcery.com