Writing reliable templated code for both `var` and `double` instantiations

Developers
7

Thanks for the clarification. What you’re looking for is something called argument dependent lookup (link to cppreference).

From the original example, it would work if you did this:

namespace stan { 
  namespace math { 
    template <typename T>
    T test(const T& x) { 
       using std::fabs;
       return fabs(x); 
    }
  }
}

Edit: this is not true. Please read the next comment for an explanation. If you were outside the stan::math:: namespace, you’d also want to add a using stan::math::fabs;. ADL will help choose the right function call for you since you put in the using statements.

It’s working for exp because I bet there’s an exp in the global namespace that’s brought in using one of your includes.

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