[boost] [random] Use of make_unsigned/make_signed

Subject: [boost] [random] Use of make_unsigned/make_signed
From: John Maddock (boost.regex_at_[hidden])
Date: 2012-03-14 14:30:43

Several of the random number distributions use make_[un]signed internally. 
However, this trait is not intended as a customization point for UDT's - 
it's only supposed to be instantiated for integer or enum types - and yes 
that's a deliberate decision that's now enshrined in the standard ;-)

Unfortunately this means that these distributions can't be instantiated on 
UDT's - big number types for example.

Since it seems that these traits are only used to obtain a type that is 
large enough to store a difference between the endpoints of a range, would 
it be possible for these to change to use something like:

namespace boost{ namespace random{

template <class T>
struct range_type : public make_signed<T>
{
};

}}

Then range_type could be [partially-] specialized for UDT's.  Note that for 
some types, there might simply not be a corresponding unsigned type at all, 
but I'm assuming that doesn't foul up the logic, as long as the type is wide 
enough?

Comments?

Thanks, John.