bob8

I did not say Vivaldi was slow, just that performance is relevant in UI. I'll give Vivaldi a try.

UI is very latency sensitive, even a couple of frames of delay can be detrimental to the feel of a UI.

Can't you have a regular vector and place the place the appended items on the even indices and prepended items on the odd? If you keep count of how many prepended and appended items you have you have identical performance to a regular vector except a worst case doubling of memory.