regex empty expression bug?

From: chengst87 (christian.engstrom_at_[hidden])
Date: 2001-12-18 11:25:08

The following program:

#include <boost/regex.hpp>
void main() {
  boost::regex aa;
  boost::regex bb(aa);
}

throws the exception boost::bad_expression("Empty expression.") when 
executed.  The reason is of course that the regex aa is empty at the 
point where it is used to initialize bb.

My quesion is: is there any particular reason for this, or should 
this be considered a bug in the regex package?

I personnaly cannot see why it should be more illegal to use an empty 
regex object to initialize another one than it was to create the 
emtpy regex object in the first place.  The analogy with other types 
would also suggest that this should be legal, since, for instance, it 
is perfectly legal to initialize a string with another string that is 
empty, or an integer with another integer that is 0.  If there are 
some arguments against this I would be very interested to hear them, 
if not, I am hereby submitting this as a bug report.