The following structure can be expected, after __switching to C++20__
* Concept **Allocator** deals with the bare memory allocation
* Concept **Factory** handles object creation and disposal by delegation
* Concept **Handle** is a ready-made functor for dependency-injection
Right now, an implementation of the ''prospective Factory Concept''
can be provided, by delegating through `std::allocator_traits` to a given
`std::allocator` or compatible object
Introduced as remedy for a long standing sloppiness:
Using a `char[]` together with `reinterpret_cast` in storage management helpers
bears danger of placing objects with wrong alignment; moreover, there are increasing
risks that modern code optimisers miss the ''backdoor access'' and might apply too
aggressive rewritings.
With C++17, there is a standard conformant way to express such a usage scheme.
* `lib::UninitialisedStorage` can now be used in a situation (e.g. as in `ExtentFamily`)
where a complete block of storage is allocated once and then subsequently used
to plant objects one by one
* moreover, I went over the code base and adapted the most relevant usages of
''placement-new into buffer'' to also include the `std::launder()` marker
...ouch this was insidious: the STL implementation for list does not
return a pointer to the element just allocated, but rather retrieves
and dereferences the back() / front() iterator after returning from emplace_back|front()
...which in case of re-entrant allocations is something wildly different
than the initial allocation. Thus a *cheap* and dirty placeholder implementation
just using a STL container is not possible, and we need at least
to code up likewise cheesy placeholder implementation by hand.
- separate allocation and ctor all
- use an inline buffer in the STL container
- explicitly handle ctor failures to discard allocation
- NOT THREADSAFE and likely WASTFUL in terms of performance
==> MockSupport_test now back to GREEN after complete refactoring
...by defining a new scheme for access to custom allocators
...and then passing a reference to such an accessor into the
JobTicket ctor, thereby allowing the ticket istelf recursively
to place further JobTicket instances into the allocation space
--> success, test passes (finally)
