Subject: Re: [PATCH 2/3] oidmap: add size function

From: Patrick Steinhardt <[email-masked]>
Date: Tue, 13 May 2025 11:48:36 +0200

On Mon, May 12, 2025 at 02:51:30PM -0400, Jeff King wrote:
> Callers which want to know how many items are in an oidmap have to look
> at the underlying hashmap struct, leaking an implementation detail.
> Let's provide a type-appropriate wrapper and use it.
> 
> Note in the call from lookup_replace_object(), the caller was actually
> looking at the hashmap's tablesize parameter (the allocated size of the
> table) rather than hashmap_get_size(), the number of items in the table.
> This probably should have been checking the number of items all along,
> but the two are functionally equivalent here since we only add to the
> map and never remove anything. Thus if there was any allocation, it was
> because there is at least one item.

I was a bit puzzled by this explanation initially. The two sizes aren't
functioally equivalent -- the table size will typically be larger than
the number of contained entries. But the thing is that we don't care for
the actual size, we only care whether the map is empty or not. And for
that those are indeed equivalent in this specific case.

Patrick