[KingOfCoders]

You didn't have a hard time with the borrow checker because you used the Rust GC? Was that the argument?

Actually I left Rust and moved to Go although I love Rust much more because every struct ended up sprinkled with Arc.

[mplanchard]

No, there’s no argument. The statement was that lifetimes aren’t that hard, and that when you do get stuck there are escape hatches. The escape hatches are especially useful when you’re still learning.

FWIW I write Rust professionally now, and in our entire codebase we have maybe four or five data structures containing Arcs, specifically where objects are spawned as Futures on other threads.

[KingOfCoders]

That would be a very interesting metric, could you grep|wc them and the locs?

[mplanchard]

Sure!

Tokei says that we've got ~76k lines of Rust.

I used ripgrep to find occurrences of `Arc::` (to exclude type signatures and only find constructors) and then just gave it a quick manual look to exclude tests and benchmarks.

This leaves me with:

- one data structure that contains general application state and contextual information, which is created at application startup and shared across all tasks/threads

- one data structure for accumulating results that is shared across threads. This is an Arc<Mutex<u64, SomeEnum>>. The less common of the two enum variants is an Arc<BTreeMap>.

- one data structure used to pass a database connection in to a context where it'll be used to spawn async tasks

All told, we've only got four places in production paths where we construct a new Arc. One of those four is only called once in the life cycle of the application, while the others are called for any given invocation.

[KingOfCoders]

You're comment made my day, thanks for your work!

[mplanchard]

Hey no problem! I was glad my guess wasn’t too far off, and it was fun to go digging to check.