Signed integer addition is only associative when overflow is defined to wrap around like unsigned arithmetic. This condition is matched here, because only debug builds panic on overflow. However, it's a bit of a gray area that the article completely ignores.

• thrance

  today at 10:27 AM

  Unlike C, Rust's signed arithmetic is fully specified to wrap around.

  • aw1621107

    today at 10:58 AM

    > Rust's signed arithmetic is fully specified to wrap around.

    Well, kind of. It's currently documented to wrap in release mode by default, but it's just that - a default. You're free to enable overflow checks in release mode (or disable them in debug if you really like oddball configurations), and either way overflow is considered a logic error that devs shouldn't rely on (and basically can't rely on when not in control of the end binary since it's the end user who controls overflow checks).

    The Rust devs are theoretically open to making signed overflow panic by default, but consider such a change unlikely unless "something materially changes" [0].

    [0]: https://github.com/rust-lang/rust/issues/47739#issuecomment-...

I'm not an expert on floating point math, but the "Does adding a small number do nothing?" example caught my eye, because the numbers used are constants, which are arbitrary precision in some languages (https://stackoverflow.com/questions/57511935/what-is-the-pur...). For instance, Go answers the question with false (but still prints out "1e+16" when you try to print 1e16 + 1): https://go.dev/play/p/mSAktWpCRJA