Re: [boost] Bug in boost::rational, no Boolean conversion

From: Daryle Walker (darylew_at_[hidden])
Date: 2005-07-17 15:31:51

On 7/17/05 1:57 AM, "Jonathan Turkanis" <technews_at_[hidden]> wrote:

> Daryle Walker wrote:
>> I'm writing a class template where the template parameter is a type
>> that should represent real numbers.  It started choking when using
>> boost::rational when I needed Boolean conversion, [...]
> 
>> Before anyone says that's proper, realize that boost::rational DOES
>> have "operator not()" defined!  This is a surprise to the typical C++
>> programmer.  Either both should be defined, or neither.  I think that
>> boost::rational should add a Boolean conversion.  (It's a quick fix,
>> and it is critical, so it should be done for this release.)
> 
> Off the top of my head, I can't think why it shouldn't be added. However,
> there might be a good reason I can't think of, and adding the operator could
> conceivably break existing code, so I don't think it's appropriate to stick it
> in a few days before release.

Boolean conversions are currently banned, so they couldn't be in existing
code.  The worry is expressions where a conversion would be higher priority
that whatever operation is currently used.  The only operations I can think
of in that category are other conversions, but a new Boolean conversion
can't cause problems because C++ allows at most one user-conversion (i.e.
the new operation is of lower priority).  If we use a member-pointer and
keep the type & values used private, then no one can name the type to grab
it directly.  The class template already defines equality operators, so we
don't have to worry about the member-pointer conversion adding inappropriate
operators, especially if we make each version of boost::rational maintain
separate Boolean types.

> I'll add it to the list of feature requests for 1.34.

I put it in our SourceForge bug tracker as Request ID #1239906, so we won't
forget.

> In the mean time, maybe you can use != 0 or !!

I have "x != T()" right now, but I want to keep the code clean.  Especially
since I specified Boolean conversion as a requirement.  (I didn't know about
boost::rational's deficiency at first.)

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT hotmail DOT com