[Boost-users] problems with C++ integer types

Subject: [Boost-users] problems with C++ integer types
From: Robert Ramey (ramey_at_[hidden])
Date: 2012-01-29 18:01:10

I'm very confused about a number of things related to C++ standard and boost 
libraries
dealing with numeric types.  Here are a few things that I'm not getting.

a) The standard says in section 18.3.2.1

"Specializations shall be provided for each arithmetic type, both floating 
point and integer, including bool.
The member is_specialized shall be true for all such specializations of 
numeric_limits."
...
"Non-arithmetic standard types, such as complex<T> (26.4.2), shall not have 
specializations."

and it section 18.3.2.4 numeric_limits members

static constexpr bool is_bounded;

"True if the set of values representable by the type is finite. [ Note: All 
built-in types are bounded.
This member would be false for arbitrary precision types.-end note ]"

So the question is: if one makes a "numeric type" like std::complex (or safe 
integer
which I'm interested in right now). Should one define a specialization for 
this new type?

The working is pretty specific, but then I can't see why "is_bounded" is in 
there since
all built-in arithmetic types are bounded.  Oh I see this now: Required by 
LIA-1.

b) boost/type_traits/is_integral.hpp

This file just specializes each arithmetic type supported by the 
implementation.

question:Why isn't it just implemented in terms of numeric limits so that 
every
thing is always consistent and never "out of sync"  It's implementation 
returns
true for only the built in types so it seems to me it should be repeating 
what
ever happens to already be in numeric_types.

c) my real interest is to implement a type "safe_integer" which can be
used anywhere an integer is used but will trap errors which occur in
the course of implicit conversions and assignements.  If I don't specialize
numeric_limits for my new "safe_integer" certain type_traits like is_signed
won't work for it.  If I do - them I"m out of sync with is_integral.hpp and
likely out of conformance with the standard - though I'm not sure what the
implications of that might be.

I'm aware that there is related work going on here - bigint and arbitrary
length integers.  How do the authors of these libraries plan to  address 
this.

There are other cases applications where this would also come up
such as modular integer<modulus> , safe_integer_range<max, min>
and who know what else.

Any useful information/insight would be appreciated.

Robert Ramey