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Or even use an array of size 3, but include the IDs in each element and linearly scan for the right ID. As the whole array will likely fit on a cache line and you want to access all three elements in a short time anyway, this is likely no slower than a hash table.

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That's what I was thinking after reading the rationale, there are plenty of options that don't involve a hash map.

That said, linearly scanning is not much different from a hash map with linear probing that has no empty slots left, so it's not necessarily obvious that the hash map actually takes that much more space.

I wouldn't expect a hash map that uses linear probing to wait until it's full (or even nearly full) before increasing the size of the table. Doing a linear scan on a hash table which is both nearly full and very large would be quite bad.

Normally I wouldn't expect it either, but if you know it caps out at single-digit numbers of elements, then it's not the worst idea.

I'd still just use a plain array, but my point was that hash maps aren't necessarily big and unwieldy.

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