5 ms·

It is silly to equate drop flags with atomic reference counting on the heap. It would be sillier to define automatic memory management in terms of conditional

It is silly to equate drop flags with atomic reference counting on the heap. It would be sillier to define automatic memory management in terms of conditional releases, (as you seem to have done) and then insist that Rust's conditional releases don't really count. Clearly, it is not really the fact that the releases are conditional that makes the difference. What is your actual definition of automatic memory management? What, in your view, is the actual semantic difference between a language that has automatic memory management and one that does not?

Manishearth 10y ago
Swift cannot implement ARC without conditional releases. Rust can. What Rust effectively does is compile an if statement into something a tiny bit more complicated (two if statements, really), in certain conditions. It doesn't need to. The if statement uses function-local information known statically, so it could be compiled in a different way without the drop flag. Basically, the condition already existed, Rust just inserts another one instead of piggybacking on the one inserted by the programmer. ARC needs new conditionals everywhere, and whether or not something will be cleared is often not obvious without looking at the whole program, and even then it could be undecidable. I can't answer for Patrick, but I don't see the term "automatic memory management" as useful as distinction, I look at it more as a spectrum, and Rust/C++ fall squarely on the "more manual" end of that.
- winstonewert 10y ago
  "I can't answer for Patrick, but I don't see the term "automatic memory management" as useful as distinction, I look at it more as a spectrum, and Rust/C++ fall squarely on the "more manual" end of that." I agree 100%. My objection was to the assertion that Rust and Swift were completely different because Swift was garbage collected and Rust was not. That's just not a helpful way of looking at it, because in many ways Swift's strategy is closer to Rust's then Java's.
  - Manishearth 10y ago
    Right, which is why in my other comment I explained why the memory management strategies make them different, and make that difference important :) type system wise they are pretty comparable otherwise; As a Rustacean who is used to nice type systems, Swift's type system is a pleasure to work with.
  - winstonewert 10y ago
    Sure there are significant differences between Rust and Swift. But characterizing that as Swift = GC, Rust = No GC, as I was originally objecting to is a pretty terrible way of describing it.
    - Manishearth 10y ago
      Right, but the significant difference does lie in the memory management thing. GC/No GC is (a) correct, according to the academic definition, and (b) a decent approximation to the difference.

Manishearth 10y ago

Swift cannot implement ARC without conditional releases. Rust can. What Rust effectively does is compile an if statement into something a tiny bit more complicated (two if statements, really), in certain conditions. It doesn't need to. The if statement uses function-local information known statically, so it could be compiled in a different way without the drop flag. Basically, the condition already existed, Rust just inserts another one instead of piggybacking on the one inserted by the programmer. ARC needs new conditionals everywhere, and whether or not something will be cleared is often not obvious without looking at the whole program, and even then it could be undecidable. I can't answer for Patrick, but I don't see the term "automatic memory management" as useful as distinction, I look at it more as a spectrum, and Rust/C++ fall squarely on the "more manual" end of that.

winstonewert 10y ago
"I can't answer for Patrick, but I don't see the term "automatic memory management" as useful as distinction, I look at it more as a spectrum, and Rust/C++ fall squarely on the "more manual" end of that." I agree 100%. My objection was to the assertion that Rust and Swift were completely different because Swift was garbage collected and Rust was not. That's just not a helpful way of looking at it, because in many ways Swift's strategy is closer to Rust's then Java's.
- Manishearth 10y ago
  Right, which is why in my other comment I explained why the memory management strategies make them different, and make that difference important :) type system wise they are pretty comparable otherwise; As a Rustacean who is used to nice type systems, Swift's type system is a pleasure to work with.
- winstonewert 10y ago
  Sure there are significant differences between Rust and Swift. But characterizing that as Swift = GC, Rust = No GC, as I was originally objecting to is a pretty terrible way of describing it.
  - Manishearth 10y ago
    Right, but the significant difference does lie in the memory management thing. GC/No GC is (a) correct, according to the academic definition, and (b) a decent approximation to the difference.