Re: [boost] rational.hpp

From: Jens Maurer (Jens.Maurer_at_[hidden])
Date: 2001-01-15 16:02:55

Jens Maurer wrote:
> Ok, now we have a nice technical problem to solve: How to allow
> for a rational(long) constructor which works even for rational<long>,
> where we have to avoid ambiguities with the copy constructor.

Option 1:  Use template specialization

Define specializations for rational<long> and rational<unsigned long>,
e.g. (abbreviated):

template<class IntType>
class rational
{
public:
  rational(IntType n = 0) : num(n), den(1) { }
  rational(long n) : num(n), den(1) { }
private:
  IntType num, den;
};

template<>
class rational<long>
{
public:
  rational(long n = 0) : num(n), den(1) { }
private:
  long num, den;
};

Option 2: Same as option 1, but define everything except the
constructors in a base class:

template<class IntType>
class rational_base
{
public:
  explicit rational_base(IntType n) : num(n), den(1) { }
  // add other stuff here
private:
  IntType num, den;
};

template<class IntType>
class rational : public rational_base<IntType>
{
public:
  rational(IntType n = 0) : rational_base<IntType>(n) { }
  rational(long n) : rational_base<IntType>(n) { }
  // nothing else needed here
};

template<>
class rational<long> : public rational_base<long>
{
public:
  rational(long n = 0) : rational_base<long>(n) { }
  // nothing else needed here
};

Hm... Looks like explicit specializations are required, because
we need to do away with one offending constructor.

Instead of long/unsigned long you may consider using boost::intmax_t
and boost::uintmax_t from boost/cstdint.hpp, although integer_test.cpp
does not seem to work on Win32 / MSVC 6.0sp4 / STLport 4.0.

Completely unrelated:
We should probably split
    rational(IntType n = 0) : num(n), den(1) {}
into two constructors, because the default-argument version needs an
implicit conversion from int to IntType, which may not exist.

Jens Maurer