alt Hacker News> So there I was, implementing a one element ring buffer. Which, I'm sure you'll agree, is a perfectly reasonable data structure.
It is, but, IMO, shouldn’t use the code for “a n-element ring buffer, with n set to 1”, similarly to how an array of booleans in many languages shouldn’t be implemented as “an arrayof Foos, with Foo set to bool”.
C++ has std::bitset and std::vector and Java similarly has BitSet and Array because using the generic code for arrays of bits is too wasteful.
Similarly, a one-element ring buffer is either full or it is empty. Why use two indexes to encode a single boolean?
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It was for a dynamically growing ring buffer that also did short-object optimization. The natural implementation was to have the capacity and the offsets stored in fixed locations and with a fixed width, and have the variable part be a union of pointer or inline byte buffer.
Depending on the element width, you'd have space for different amounts of data in the inline buffer. Sometimes 1, sometimes a few more. Specializing for a one-element inline buffer would be quite complex with limited gains.
In retrospect trying to use that as a running gag for the blog post did not work well without actually giving the full context, but the full context would have been a distraction.
> C++ has std::bitset and std::vector
Notably, this is not the case. C++ std::vector is specialised for bools to pack bits into words, causing an untold array (heh) of headaches.
And "wasteful" is doing a lot of lifting here. In terms of memory usage? Yes. In terms of CPU? The other way around.
> C++ has std::bitset and std::vector and Java similarly has BitSet and Array because using the generic code for arrays of bits is too wasteful.
Rather infamously, C++ tried to be clever here and std::vector<bool> is not just a vector-of-bools but instead a totally different vector-ish type that lacks many of the important properties of every other instantiation of std::vector. Yes, a lot of the time you want the space efficiency of a dynamic bitset, rather than wasting an extra 7 bits per element. But also quite often you do want the behavior of a "real" std::vector for true/false values, and then you have to work around it manually (usually via std::vector<uint8_t> or similar) to get the expected behavior.