Vec is asymmetric with memory handling

[burntsushi]

@tczajka

I would think in most user cases the memory allocation strategy isn't that important. malloc is not that slow. So you have to count many of these as a tie.

You would think so, but it's not true in practice. I've done this optimization so many times I can't count it. It's so common that it makes its way into API design. (e.g., "Provide a &mut borrow to this thing so that it can be reused.") So no, I absolutely do not count these as a tie.