class SizeTracker

SizeTracker is a partially specialized internal class used to track (or

explicitly to not track) the size of Lists in the fidl::internal_wavl:: containers. Its

behavior and size depends on the SizeOrder template parameter passed to it.

Please note that to use this class, containers must (sadly) derive from it, they

cannot simply encapsulate it. The SizeOrder::N version of the tracker is

nominally of 0 size, however 0 sized members of a struct/class are not allowed

in C++. Attempting to put a 0 sized member into a class results in at least

1 byte of size impact, which changes the size of the entire object.

0 sized base classes, however, are totally fine. So, if we encapsulate a

SizeTracker

<SizeOrder

::N>, then our container gets bigger for no reason, but

if we derive from one, then our container stays the size that we expect it

to.

static_assert tests for this exist in the non-sized doubly and singly linked

list tests.