Re: [boost] [complex] Feedback and Potential Review Manager

Subject: Re: [boost] [complex] Feedback and Potential Review Manager
From: John Maddock (boost.regex_at_[hidden])
Date: 2012-04-30 04:37:10

Another comment to add to Chris's, you have code like this:

template<typename T>
inline complex<T> polar(const T& r, const T& theta)
{
    return complex<T>(r*cos(theta), r*sin(theta));
}

Which will either:

* Not compile if the compiler strictly adhers to the std and doesn't inject 
cos and sin into the global namespace, or:
* Silently do the wrong thing when T is a long double - truncate r and theta 
to double and call ::cos(double) etc.

You can't just add a std:: prefix to all the calls either, as then it won't 
work with user-defined types whose functions aren't in namespace std.

So instead you need:

template<typename T>
inline complex<T> polar(const T& r, const T& theta)
{
   using std::cos;  using std::sin;
    return complex<T>(r*cos(theta), r*sin(theta));
}

In Boost.Math we found this trap so easy to slip into that:

* We have a macro "BOOST_MATH_STD_USING" which adds all the possible using 
declarations to the start of a function.
* A concept-checking type std_real_concept, which when passed to a function 
like the above, won't compile unless it's done right.

HTH, John.