> If I type the next letter of the top match, it should remain the top match.
I find these types of inductive rules might be a better way to express how autocomplete should work (given a limited universe of suggestions).
Trying to switch to 1Password is somehow even more irritating. Typing "1p" reasonably suggests 1Password. If I continue typing "1pa", however, I'm given the hilariously unrelated knowledge that 1 Pascal is equal to 0.0075 Torrs. Pressing return then takes me a Google search (in Safari, which isn't even my default browser) for "1pa" which gives me yet another pressure unit conversion, 1 Pa = 1e-5 bar.
So "de" might suggest "defaultdict" but if I add an "f" and auto complete it gives me a function template.
This is trivial to do on exact contexts (like start menus - why none gets this?). It's ok to wait until the user enters some letters to start showing options, it's also ok to limit the number of results as long as you say there are more somewhere. What is not ok is to show a single match, and then after the user press another key show two matches, with the first one gone.
Distance based matching can't strictly follow this rule, but if you are optimizing one, it is a good goal to get approximately right.
How would this not always be the case anyway given the other rules in place?
I can't imagine anything faster than Spotlight other than the few times where it's reindexing.
Even then its hard to even define the next letter. With sub-sequence matching something like "gsl" might be displayed as "[g]et[D]isplay[L]ist" with items in brackets highlighted. No real next letter in this case.