On Sunday, 9 July 2023 at 20:24:24 UTC, Cecil Ward wrote:
Before I posted a question about avoiding unnecessary
allocs/reallocs when adding entries to an array like so
uint[ dstring ] arr;
when I build it up from nothing with successive insertions.
The array is accessed by a key that is a dstring. I was told
that I can’t use .reserve or the like on it? Is that correct?
My memory fails me, powerful pain drugs.
Is there an alternate method I could use ? To be honest, the
number of entries is likely to be extremely modest, so this is
not a huge performance issue, six entries would be considered
quite a lot. The string keys are probably not very very long.
But I’m learning good habits for the day when I might have a
bigger such database.
From the spec it sounds as though (but good luck testing for
sure) that if you have (for example) 6 big dummy key-value pairs
in the AA to begin with, then if you use `.clear` it "Removes all
remaining keys and values from [the] associative array. The array
is not rehashed after removal, __to allow for the existing
storage to be reused.__"
([source](https://dlang.org/spec/hash-map.html#properties)) I'm
not 100% sure this would work how you want, and it's such a hack,
but it's something.
D has a few user-made hash-map libraries, so it might be worth
investigating those to see if they offer a pre-allocation method,
too.
