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Subject: Re: [boost] [complex] Feedback and Potential Review Manager
From: John Maddock (boost.regex_at_[hidden])
Date: 20120430 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 userdefined 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 conceptchecking type std_real_concept, which when passed to a function
like the above, won't compile unless it's done right.
HTH, John.
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