A couple of questions about arrays and slices

[Cecil Ward]

On Saturday, 24 June 2023 at 07:36:26 UTC, Cecil Ward wrote:
> Jonathan, is it possible that I wanted one thing and got 
> another? My description in the earlier post was of the _aim_ of 
> the program. What I ended up with might be something else? I 
> wanted an array of uints whose values are the results/outputs 
> of the mapping function. Since it is keyed by strings I assumed 
> that the runtime generates some kind of hash for fast lookup 
> when I ask it to retrieve an entry by the string (key) 
> associated with it. I assumed that in some sense the hashing 
> was sort of separate with some degree of independence from the 
> underlying array, if that makes sense. The lookup is just 
> assumed to be fast but how it is done we don’t really care. I 
> just wanted to expand the array as I did successfully elsewhere 
> with reserve, as I built this structure by successive additions 
> of data. I have a number of strings and the map is meant to 
> output the ordinal number in which I first saw them, 
> zero-based. Then I want to come back and randomly look up one 
> ordinal given a string preferably with a very fast lookup. The 
> number of entries can not practically be more than 30, and even 
> that would be highly unusual, maybe ten is the practical limit 
> in my particular case, so it’s hardly MySQL.

I just realised something, your point about altering the table 
and having to rehash, is well taken. I hadn’t considered that. 
The reason for my foolishness in failing to realise that I’m 
asking the impractical is my pattern of usage. I add all the 
entries into the mapping table and have no interest in any 
lookups until it is fully built. Then a second function starts to 
do lookups while the data remains unchanging and that usage 
pattern can be guaranteed. I could even idup it if that would 
help, as copying < 32 uints wouldn’t take forever. A typical 
value would be a mere 5 or less. I only picked 32 to be 
completely safely ott.