C++ PATCH: Disallow floating-point literals in integral-constant expressions

[Mark Mitchell]

Joe Buck wrote:
> On Mon, Jan 31, 2005 at 05:52:24PM -0800, Mark Mitchell wrote:
> 
>>It is not true that if GCC X accepted a piece of code, but GCC X + 1 
>>does not, then we have removed a feature and must deprecate, etc.
>  
> In general this is true, but not in this case.  You have removed a
> well-known g++ extension that dates back to 1990, the first year that I
> used g++.

I was using G++ at that point too, but I don't remember ever trying to 
do this particular thing.  Perhaps I generally tried to avoid 
non-standard usage (in the ARM sense, in those days) more than other 
people using G++.

In any case, I suggest we hndle it as follows.  The current codebase (as 
of this morning) will issue an error only with -pedantic.  It will do 
that both for occurrences of floating-point literals in integral 
constant expressions (that are not cast to an integral type) and for 
initializations of static data members of floating-point type.

In other words, with -pedantic, we warn about both data members in:

   struct S {
     static const int i = 3.0; // Invalid integral constant expression.
     static const double d = 0; // Invalid data member type.
   };

With -fpermissive (or no option) we accept both lines.

So, I think the current codebase is acceptable to you.

This particular extension is very unlikely to cause us to do something 
really bad.  (Other things that we used to accept in what should have 
been integral constant expressions did cause real confusion, including 
ICEs.)  Also, I cannot think of any way in which allowing floating-point 
literals in integral constant expressions could change the meaning of a 
conforming program.  So, the current state is acceptable to me too, 
except that instead of "if (pedantic) error (...)" I should probably use 
  "if (pedantic) pedwarn (...)".

I think that the remaining action item, then, is to document this 
extension.  Would you please document both the extension to allow 
floating-point literals in integral constant expressions and the 
extension to allow initialized static data members of floating-point type?

Thanks,

-- 
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
(916) 791-8304