APL\360

On Wed, Jan 20, 2021 at 02:05:37PM -0700, ben via cctalk wrote: [...] You're describing a failing in C and similar languages stuck in the 1960s. Here's a Rust method that does add-exposing-carry: https://doc.rust-lang.org/nightly/std/primitive.u32.html#method.overflowing… The documentation doesn't explicitly say "carry" because Rust is architecture-neutral and it's down to LLVM to decide how to express it in machine code, but on x86 (and probably ARM) the boolean return value comes directly from the carry flag. You "don't believe in objects" yet then describe a problem which only exists due to the lack of them and then present OO pseudocode to solve it. A lot of OO languages suck of course, but the fundamental idea of encapsulation is not the bit that sucks. Here's it in Rust, where it takes in an arbitrary array (pedantically, "slice", a (pointer, element count)-tuple) and determines its length at runtime: pub fn clear_indexed(array: &mut [usize]) { for index in 0 .. array.len() { array[index] = 0; } } (The code for C-style fixed-length arrays looks broadly similar but has a bit more boilerplate because they're less useful.) Iterating over indices is generally discouraged for a number of reasons, not least being that the index may be out-of-bounds, but also because it can inhibit vectorisation or parallelisation. You have no choice in broken languages such as C, but many languages provide some notion of iteration which guarantees to not go out-of-bounds: pub fn clear_iterator(array: &mut [usize]) { for elem in array { *elem = 0; } } Both code fragments generate equivalent assembly in this trivial example because the Rust compiler could prove at compile time that the index variable can't go out-of-bounds. In more complex real-world code it cannot reliably do so and will insert a run-time check which aborts if the index is out-of-bounds. Or if it's C, trundle on and corrupt things. Oddly enough, the state of the art has moved on a bit in the half-century since C was invented. It's just that quite a lot of programmers haven't yet noticed.