C++ for Scientists - Technische Universität Dresden

5.2. PROVIDING TYPE INFORMATION 137
struct Magnitude
{
typedef double type;
};
template
struct Magnitude
{
typedef float type;
};
template
struct Magnitude
{
typedef double type;
};
Admittedly, this is rather cumbersome.
We can abbreviate the first definitions by postulating “if we do not know better, we assume
that T’s Magnitude type is T itself.”
template
struct Magnitude
{
typedef T type;
};
This is true for all intrinsic types and we handle them all correctly with one definition. A slight
disadvantage of this definition is that it incorrectly applies to all types whose type trait is not
specialized. A set of classes where we know that the above definition is not correct, are all
instantiations of the template class complex. So we define specializations like:
template
struct Magnitude
{
typedef double type;
};
Instead of defining them individually for complex, complex, . . . we use a templated
form to treat them all
template
struct Magnitude
{
typedef T type;
};
Now that the type traits are defined we can refactor our function to use it:
template
T inline min magnitude(const T& x, const T& y)
{
using std::abs;
typename Magnitude::type ax= abs(x), ay= abs(y);
return ax < ay ? x : y;
}