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Comment by cesarb | Hacker News Reader

> ...while I agree, for many C++ and Rust coders statements like this are pure heresy ;)

It's a matter of definitions. For many people, "garbage collection" refers only to tracing GC, and reference counting is a separate category. In my experience, that's the common usage; insisting that "reference counting is formally (in some paper from the last century) also defined as a form of GC" will not magically change the opinions "many C++ and Rust coders" have about tracing GC. In fact, I'd say that insisting on this nomenclature point only weakens the whole argument; tracing GC should stand on its own merits, and not on depend on some nomenclature equivalence to be accepted (if quibbling about nomenclature is your strongest argument, your arguments are weak).

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There's no need to "change opinions". People who work on GCs know that reference counting and tracing are the two general GC strategies. The only people who don't think of refcounting as a GC are people who simply aren't familiar with GCs and how they work. If they also think refcounting has lower latencies (let alone higher throughput) than tracing, then they're also just wrong. No one needs to "insist" on the GC nomenclature. You're either familiar with it or you're not (and since most people are not, they commonly make mistakes on the subject). Also, given that tracing GCs are used by ~90% the market, they hardly require justification anymore; they've won by a large margin over the application space (which constitutes most of software). However, it's nice to occasionally educate those unfamiliar with the subject on GC algorithms and nomenclature.

> Also, given that tracing GCs are used by ~90% the market, they hardly require justification anymore; they've won by a large margin over the application space (which constitutes most of software).

Tracing GCs have clearly proven themselves and are everywhere (JVM, CLR, Go, Dart, OCaml, etc.) but we can't ignore that the Apple ecosystem (Swift) is using ARC. That's a significant share of the "market". Python and Ruby also use reference counting, but I don't think anyone is considering them state-of-the-art GC.

Except that obligate ARC ala Swift has even lower throughput than obligate tracing GC. It's the worst possible choice unless you really care about low-latency and deterministic freeing of resources (and even then, using RAII for common tree-like allocation patterns like Rust does will perform better).

You're right, I should have said "languages where GC is the primary means of managing heap memory are used by 90% of the market" rather than focused on a specific algorithm.

Yes, this is quite fascinating how GC replaced manual memory management in most apps over the last 20~30 years.

Ruby does not use reference counting. It has a mark and sweep generational gc that is incremental and use compaction. I doubt it would be state of the art, but it is not too bad nowadays.

My mistake. Thanks for correcting.

I have to wonder whether some of this is semantic drift over time or context. My recollection since undergrad (a few decades ago) involves treating “garbage collection” as referring to tracing garbage collection, and “reference counting” as a separate mechanism. There is still a term for the category including both, only that term is not “garbage collection” but “automatic memory management”. But what I see nowadays is closer to what you describe.

Automatic memory management is more general than that, it also includes stack allocation.

I agree; I meant “including” in the non-restrictive sense, not “including only”. Stack allocation is a special case where the lifetimes are arranged in a convenient way—see also escape analysis in languages where stack allocation isn't explicitly supported at the language level but can be added by the compiler.

If anything, the drift is towards GC being only tracing as it is so dominant in the languages that are normally considered having GC. But before C++ (via boost) introduced shared pointers, and Swift ARC, I'd expect the separation to basically not exist.

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