has_trivial_destructor improvable?

[Jonathan Wakely]

On 22 February 2012 15:55, Hite, Christopher wrote:
>
> Hi, does has_trivial_destructor<> and co depend on compiler magic?

Yes.

> Is it possible to detect empty deconstructors/constructors.  The reason I ask is because I'd like to make better placeholders for a boost::optional implementation using new unions from N2544.
>
> template<typename T>
> union placeholder{
>        T v;
>        placeholder() {}   // breaks has_trivial_constructor
>        ~placeholder (){} // breaks has_trivial_destructor
> };
>
> Is improving these possible or is there some conceptual problem with a circular reference?

I don't understand the question, sorry.

What do you mean "breaks has_trivial_constructor" ?

Do you just mean has_trivial_default_constructor::value is false?

If you declare the constructor and destructor as defaulted then they
will be trivial for placeholder<X> if they are trivial for X:

       placeholder() = default;
       ~placeholder () = default;