Here’s a simple non-constexpr-friendly Optional type. (Godbolt.)

template<class T>
class [[trivially_relocatable(std::is_trivially_relocatable_v<T>)]] Optional {
~~~~
  alignas(T) char data_[sizeof(T)];
  bool engaged_ = false;
};

Here’s a simple C++20 constexpr-friendly Optional type. (Godbolt.)

template<class T>
class [[trivially_relocatable(std::is_trivially_relocatable_v<T>)]] Optional {
~~~~
  union {
    char pad_;
    T t_;
  };
  bool engaged_ = false;
};

Here’s a simple and trivially relocatable MoveOnlyCallable type. This is like std::move_only_function<int(int) const>, except that the “take int and return int” part is hard-coded, for simplicity. (Godbolt.)

Martin Gardner’s “Mathematical Games” column of April 1979, on the subject of Harary tic-tac-toe, gives Frank Harary’s own pet names for the five free tetrominoes, or “order-4 animals,” as Harary called them. This reminded me of the meme assigning (fake) names to the Tetris pieces.

On StackExchange, someone asks why programmers talk about “calling” a function. Several possible allusions spring to mind:

• Calling a function is like calling on a friend — we go, we stay a while, we come back.
• Calling a function is like calling for a servant — a summoning to perform a task.
• Calling a function is like making a phone call — we ask a question and get an answer from outside ourselves.

The true answer seems to be the middle one — “calling” as in “calling up, summoning” — but indirectly, originating in the notion of “calling for” a subroutine out of a library of subroutines in the same way that we’d “call for” a book out of a closed-stack library of books.

Way back in 2022, I got the idea to do the Martin Gardner thing — to collect a few of the best posts I’d written for this blog and publish them as a proper paper book. I chickened out at the time, but this month I decided the stars were right to revisit that old project and finally publish my first collection of Essays on Modern C++.

I’m just now getting around to blogging this snippet from March 2024 (hat tip to Chip Hogg). Apparently some units libraries — things like Au and mp-units — find it useful to represent linear combinations of units as the products of primes; for example, if you represent “meters” as 2 and “seconds” as 5, then “meter-seconds” is 10. Or at least that’s the general idea, I think. Don’t quote me on that part.

This means there’s a market for fast compile-time versions of the functions next_prime_after(p) and prime_factors_of(c). Chip even went so far as to propose that vendors should provide “largest prime factor of c” as a builtin; see P3133 “Fast first-factor finding function” (February 2024). I said, “You don’t need the vendor to do your factoring; you can write that in general-purpose C++ already!”

Today I learned that the New York Public Library has a blog, on which, many years ago, curator Douglas Reside had a “Musical of the Month” series where he posted old libretti, recordings, and other paraphernalia. Sadly the NYPL’s current website design lacks any coherent indexing or tagging system: no full-text search, no search by author, etc. So, for my own benefit and the benefit of posterity, here are direct links to all of the NYPL “Musical of the Month” blog posts — at least, all of them I could discover via public indices. If you discover any more, please tell me and I’ll add them here!

Charles Haddon Spurgeon, whom we met in yesterday’s post, tells the following “Spartan saying” (Plutarch 234D) better than Plutarch does:

From John Cooper Mendenhall’s “Aureate Terms” (1919):

Who dare call the clerks blind who saw only the golden side of the shield?

This is a reference to a fable originating with Joseph Spence (writing as “Sir Harry Beaumont”) in Beaumont’s Moralities (1753).

All C-style programming languages have too many levels of operator precedence. This confuses their programmers, who have to remember not just the basic PEMDAS stuff but the really arcane precedences, too:

“Not great, Bob!”

I’ve recently engaged in book-club discussions on the following classic papers in the field of “artificial intelligence”:

Mark A. Peterson’s essay “Dante and the 3-sphere” (Am. J. Phys. 47(12), December 1979) suggests that when, in Paradiso 27, Dante looks from the starry sphere upward in the direction of the Empyrean and downward in the direction of Earth, and when he sees that nine concentric circles of angels above mirror the nine concentric planetary spheres below, he is “groping for a language to express an idea conceived intuitively and nonverbally” — namely, the idea of “how a 3-sphere would look from its equator.”

In HBO’s Bored to Death episode S2E5 “Forty-Two Down,” protagonist Jonathan Ames (Jason Schwartzman) introduces himself to his target Vikram (Ajay Naidu) by asking his help with that day’s New York Times crossword. We get two brief shots of the crossword itself. The first, a closeup, is just enough to irk the crossworders in the audience, as we see a plethora of unkeyed letters. The second medium shot shows that the black squares in this asymmetric grid spell out the word “HIT.” (Or does the black blob in front of the “H” represent a fourth letter?)

The episode aired 2010-10-24, but the Times shown is mostly the issue of Wednesday 2007-11-14: the facing column contains Mike Hale’s review of the TV show Kenny vs. Spenny, and the “Answer to Previous Puzzle” at lower left is indeed Fred Piscop’s puzzle of 2007-11-13. The crossword, however, is completely doctored — I see no resemblance to the Jim Page puzzle that actually ran on that date. The clues (which do not match the grid) are hilariously zany!

Recently I discovered that besides the various libraries using P1144-style (or occasionally P2786-style) trivial relocatability, there are also at least two that use P1029R2-style “trivial destructibility after move.”

This blog post demonstrates the difference between is_trivially_relocatable and is_trivially_destructible_after_move.

Back in 2021, I wrote that “Semantically ordered arguments should be lexically ordered too.” Two minor updates in that area, which are large enough to deserve a post of their own.

In December, Kory Mathewson tweeted this puzzle-creation challenge:

Create a 5x5 crossword puzzle with two distinct solutions. Each clue must work for both solutions. Do not use the same word in both solutions. No black squares.

Here’s my offering; solutions given at the end of this post.

A perennial question on the cpplang Slack: “When I call v.clear() on a vector, does that hang onto the heap allocation, or free it?” The short answer is: “It hangs onto the allocation. Follow up with v.shrink_to_fit() if you need the allocation eagerly returned.” Now here’s the long answer!

In 2024, for the first time, I kept a record of the media that I took in this year. Well, not “media” in the news-media sense (however relevant that might have been), but in the sense of books, films, stage shows; and to a lesser extent, journal articles, magazines, TV series, and long-form online content.