[FR] Add std::function::target() equivalent

[psiha]

...yet without a separate vtable call entry:

• a void * returning version (the user has to know what is actually inside)
• add a simple boolean to the vtable/meta object: specifying whether the assigned target is in the SBO (and so you return a pointer to the SBO) or on the heap (so you return the pointer stored at the begining of the SBO, I suppose)
  (and/or take into consideration [FR] SBO-only targets #66)

[mingxwa]

a void * returning version (the user has to know what is actually inside)

Since most existing polymorphic wrappers in the standard do not support target(), there is no plan to add to proxy. On the other hand, with the current implementation of proxy, it is not trivial to dereference the target without a virtual dispatch.

add a simple boolean to the vtable/meta object

It can be done with reflection. Please refer to our unit tests as an example (exactly observes SBO).