vector / vector_ext swap function

[mike919192]

I noticed that the vector classes are missing swap() functions and I also saw there was a similar issue #1068 . I started doing a little experimentation but I want to check on some design questions before going too far.

vector_ext swap could be implemented by swapping the pointers, similar to the previous issue. But I think that vector with internal storage must do per element swap and resizing. Then also for swapping between vector and vector_ext, again per element swap and resizing would need to be done.

Let me know if there is any problem with this approach.

The STL api for reference:

https://en.cppreference.com/w/cpp/container/vector/swap.html

[jwellbelove]

vector_ext could be swapped by just swapping pointers, and you are right about a vector <=> vector_ext swap.

There is a larger question, that I have tried to look at in the past, about move for vector_ext. At the moment a move means to move the elements in the vector_ext, not 'stealing' the storage.

If a swap on a vector_ext means swapping the pointers, then it could be argued that a move should do something similar.

Unfortunately this could be a breaking change, as currently a user can be sure that the buffer address stored in a vector_ext will never be changed. This expectation is also broken with a swap that swaps pointers.

If I were to implement low overhead moves/swaps for _ext containers then I think this should be done in a major release, with a big warning to users that want to upgrade.

[mike919192]

Yeah I also had the same thought about the move constructors, but I didn't mess with them yet because of the breaking change.

Do you want to introduce the per element swap and resizing for ivector and the derived classes first? Then later implement the swapping pointers for the _ext classes and breaking change to move constructors.

The only concern I had was it might be confusing to someone when the elements are swapped versus when just the pointers are swapped. But in the end I don't think its too bad.

Then everything probably also applies the string and string_ext as well.