Re: [eigen] static_cast versus constructor

[Bob Carpenter <carp@xxxxxxxxxxx>]

On 8/27/12 5:44 AM, Gael Guennebaud wrote:
> Hi,
>
> our default implementation for the .cast<NewType>() function makes use
> of static_cast as in Eigen/src/Core/MathFunctions.h:395:
>
> template<typename OldType, typename NewType>
> struct cast_impl
> {
>    static inline NewType run(const OldType& x)
>    {
>      return static_cast<NewType>(x);
>    }
> };
>
> Would not it be better to use constructors:
>
> template<typename OldType, typename NewType>
> struct cast_impl
> {
>    static inline NewType run(const OldType& x)
>    {
>      return NewType(x);
>    }
> };
>
> which is more likely to be accepted by custom scalar types. Does
> anyone see any drawbacks of such a change?

If the second impl with the ctor works, so will the
first.  The full set of rules for static_cast are:

http://en.cppreference.com/w/cpp/language/static_cast

- Bob