[p0nce]

> On the theoretical side, not reasoning about ownership means sharing data betweent threads is done with copies (slower) or locking (slower and error prone); if you know about ownership you can share references to data while it can't be mutated for free.

I don't think it follows and it's rather the reverse: it what I share has a global owner (ie. the GC), I don't have to lock or copy by definition: once it stops being reachable it will be collected. That's why some lockfree algorithms are enabled by the GC. With ownership you would have to have a unique owner, or reference counts. GC does require write barriers or stop-the-world though so let's say it's a draw :)

> Ownership is also important for any non-memory resource (file handles, mutexes, etc). GCs release those "whenever", maybe never, unless you close manually.

Yeah, it's a big problem that the GC even attempts poorly to close them. But D has scope guards and RAII builtin so for the 50% of non-memory resources you still have to think about ownership indeed. That's more complicated that the C++ situation. But realtime it does not prevent, you may well find yourself having more time to optimize :)

[jjnoakes]

> if what I share has a global owner (ie. the GC), I don't have to lock or copy by definition

Then how you do avoid data races? Two shared references which can mutate your shared data requires either a copy, a lock, immutability, or a single writer.

[p0nce]

I use "parallel foreach", sometimes worker queues, implicit single writer... like in C++. It sounds like you think only Rust-style ownership can avoid data-races. Sure, if you want the type system to do it. For me discipline is enough and I've seen it work in teams too. Not seeing such a problem really.

[jjnoakes]

Nothing specific to Rust, although Rust encodes in the type system what I usually have to keep track of mentally, which is nice.

Trivially parallel algorithms do benefit from constructs like "parallel foreach" and implicit single writers, but in general, one either has to stick to those models (where the cognitive overhead is low but manageable) or if one ventures into more complex territory, one has to either deal with a higher mental complexity (ownership or locks), performance degradation (copying), or immutable data (if it fits your problem and doesn't decrease performance, win-win).

My argument is simply that GC doesn't fix everything, and the mental overhead of tracking ownership of memory (to me) isn't a huge burden, especially since I have to do it for non-memory resources and memory resources shared between threads already.

I'm not against a GC - I like languages that mix GC and non-GC side-by-side - because sometimes I do want to just forget about my memory, but only if it fits my problem domain. But I don't think GC beats non-GC hands-down for-all-cases.