Excessive memory operations, can I borrow as mutable all the way down the chain?

Question

Is there a way to borrow as mutable all the way down the chain and return ownership to config? The memory operations here seem really excessive to update a single variable.

The code is working as expected but coming from high level languages it seems a little "hacky". Am I on the right track? The documentation is a little sparse on this library.

// Read Config File let mut file = File::open("config.yaml").unwrap(); let mut contents = String::new(); file.read_to_string(&mut contents); // Get Mutable 'endpoints' let mut docs = YamlLoader::load_from_str(&contents).unwrap(); let mut config = docs[0].as_hash().unwrap().clone(); let mut endpoints = config[&Yaml::from_str("endpoints")].as_vec().unwrap().clone(); // Find the correct 'endpoint' for (i, endpoint) in endpoints.clone().iter().enumerate() { let mut endpoint = endpoint.as_hash().unwrap().clone(); if endpoint[&Yaml::from_str("name")] == Yaml::from_str("Current Name") { // Found the endpoint, let's update it's name endpoint.insert(Yaml::from_str("name"), Yaml::from_str("New Name")); endpoints.insert(i, Yaml::Hash(endpoint)); config.insert(Yaml::from_str("endpoints"), Yaml::Array(endpoints.clone())); } }

Not sure at all, but I would try using as_mut on the options I guess. Doubtful it'll work the whole way though. — ShadowMitia
– ShadowMitia, Commented Jul 22, 2021 at 18:06
Thanks for the tip, and I did try using as_mut. However i kept running into this error: temporary value dropped while borrowed, consider using a 'let' binding to create a longer lived value This does not work: docs[0].as_hash().as_mut().unwrap(); Am I using as_mut incorrectly? I think unwrap may be to blame here? — Banned Patriot
– Banned Patriot, Commented Jul 22, 2021 at 18:52
unwrap would be causing the errors. But I'm not sure what to do here... The other possibilty would be to use an if let or a match to take out the values? — ShadowMitia
– ShadowMitia, Commented Jul 22, 2021 at 19:03
after playing around a bit more. It seems 'as_hash' always returns an immutable borrow. The library also exposes into_hash(), but it looks like this attempts to move it. — Banned Patriot
– Banned Patriot, Commented Jul 22, 2021 at 19:15
Thanks for pointing me in the direction of match. Using this in combination with borrow_mut seems to be doing exactly what I was looking for. From what I can tell this should avoid duplicating any data in memory now correct? — Banned Patriot
– Banned Patriot, Commented Jul 22, 2021 at 20:13

John Kugelman · Accepted Answer · 2021-07-22 21:25:42Z

This is working, and I think solves all the pitfalls of my previous code.

let mut docs = YamlLoader::load_from_str(&contents).unwrap(); let mut config = docs[0].borrow_mut(); if let Yaml::Hash(hash_map) = config { if let Yaml::Array(endpoints) = hash_map[&Yaml::from_str("endpoints")].borrow_mut() { for endpoint in endpoints.iter_mut() { if let Yaml::Hash(endpoint) = endpoint.borrow_mut() { if endpoint[&Yaml::from_str("name")] == Yaml::from_str("Current Name") { endpoint.insert(Yaml::from_str("name"), Yaml::from_str("New Name")); } } } } }

Collectives™ on Stack Overflow

Excessive memory operations, can I borrow as mutable all the way down the chain?

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related