Compile-time solution to detect that an Eigen object does not have an eval() member?

Question

Most Eigen classes have an eval() method that force their evaluation. Some classes don't, for example matrix decompositions. Is there a way to distinguish between these classes at compile-time?

[Possible duplicate](http://stackoverflow.com/questions/1966362/sfinae-to-check-for-inherited-member-functions). — rodrigo, Jan 20 '14 at 23:10
I was aware of that answer, but I was looking for an eigen-specific solution. — yannick, Jan 20 '14 at 23:20
classes that have `eval()` probably inherit from some class I'm not aware of. But your solution is cool I must admit. — yannick, Jan 21 '14 at 07:02

score 2 · Accepted Answer · answered Jan 20 '14 at 23:30

2

You can define your own trait which uses SFINAE to determine this:

namespace detail
{
    template<typename T>
    auto has_eval_impl(void*)
        -> decltype(std::declval<T>().eval(), std::true_type());

    template<typename T>
    auto has_eval_impl(...) -> std::false_type;
}

template<typename T>
struct has_eval : decltype(detail::has_eval_impl<T>(nullptr)) { };

answered Jan 20 '14 at 23:30

David G

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why do you need to pass arguments to `has_eval_impl`? – yannick Jan 21 '14 at 07:31
1

@yannick Overload resolution only works between functions with parameters. If I leave both parameters empty the compiler will tell me that I can't overload based on the return type. – David G Jan 21 '14 at 12:57

Compile-time solution to detect that an Eigen object does not have an eval() member?

1 Answers1