static_vector | resizable vector with fixed capacity

I have an application that I want to minimize dynamic allocation for efficiency.

I'm leaning forward using boost::static_vector in one of my classes for that reason. I'm not sure yet exactly how big my array will need to be to accommodate most situations but there are always exceptions...

Instead of discarding the input that would require more space than what my static_vector can store, I would like to fall back on std::vector to handle those exceptions.

A pattern that I commonly use in my classes design, is that I provide its input to the constructor to populate its container, then I provide a getter function that returns a const reference to the inner container.

The possibility that the class might use one or another container is causing a mental blind spot in me.

What would be the best way to offer access to the class elements?

I have come up with few ideas but none are truly satisfactory...

1. Make my class a container using the proxy/facade pattern I'm too lazy for doing that and this is not practical if I want to apply this static_vector/vector solution everywhere...

2. Place the burden on the class user ie.

I already heard that std::vector::iterator can simply be T* instead of an iterator class.

But is it really legal?

Pointer arithmetic only applies to array and std::vector doesn't create array object (T[]) but contiguous objects (via placement new).

Moreover I think that std::launder would even be required (C++17) to access individual element (as we can read in comment of static_vector example of std::aligned_storage).

I think it is roughly equivalent to following that I think is undefined behavior.

consider the following example of a compile-time "vector".

I am training a custom NER model from scratch using the spacy.blank("en") model. I add custom word vectors to it. The vectors are loaded as follows:

tl;dr: I think my static_vector has undefined behavior, but I can't find it.

This problem is on Microsoft Visual C++ 17. I have this simple and unfinished static_vector implementation, i.e. a vector with a fixed capacity that can be stack allocated. This is a C++17 program, using std::aligned_storage and std::launder. I've tried to boil it down below to the parts that I think are relevant to the issue: