https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61909
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to lukeocamden from comment #2)
> (In reply to Jonathan Wakely from comment #1)
> > This is by design.
>
> I don't really follow - do you mean a consequence of the design, or does the
> standard mandate copying/moving the object into the heap, or does using the
> heap have some other benefit?
None of the above.
I mean the author of our std::function intentionally chose to only avoid the
heap for function pointers
/**
* Trait identifying "location-invariant" types, meaning that the
* address of the object (or any of its members) will not escape.
* Also implies a trivial copy constructor and assignment operator.
*/
template<typename _Tp>
struct __is_location_invariant
: __or_<is_pointer<_Tp>, is_member_pointer<_Tp>>::type
{ };
...
static const bool __stored_locally =
(__is_location_invariant<_Functor>::value
&& sizeof(_Functor) <= _M_max_size
&& __alignof__(_Functor) <= _M_max_align
&& (_M_max_align % __alignof__(_Functor) == 0));
