[Someone]

> 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?

[cpgxiii]

> 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.

[jsnell]

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.

[andrepd]

> 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.

[mbel]

> In terms of CPU? The other way around.

That depends on your architecture and access pattern. In case of sequential access, packed bools may perform better due to arithmetic being usually way cheaper than memory operations.