Does PathBuf::from(&some_other_pathbuf) clone the data of some_other_pathbuf?

Question

I'm writing a custom_rename function that receives a String and an immutable reference to a PathBuf:

fn custom_rename(new_name: String, old_path: &PathBuf) {
    let mut new_path = PathBuf::from(&old_path);
    new_path.pop();
    new_path.push(new_name);
    std::fs::rename(old_path, new_path).expect("error");
}

Does the PathBuf::from() function clone the data of old_path? According to The Rust Programming Language, Rustaceans try to avoid cloning.

While Rustaceans do try to avoid cloning, using a `PathBuf` is explicit instruction to make a copy, typically because (as in the included code) we are about to modify the value or prolong its lifetime (e.g. send it to a thread). — user4815162342, Aug 18 '20 at 18:51

score 3 · Accepted Answer · answered Aug 18 '20 at 18:08

3

Yes, a PathBuf owns the data. The only way to own the data when presented with a reference is to clone it.

I'd write this as

use std::{fs, path::Path};

fn custom_rename(new_name: &str, old_path: &Path) {
    let mut new_path = old_path.to_owned();
    new_path.pop();
    new_path.push(new_name);
    fs::rename(old_path, new_path).expect("error");
}

See also:

Is it more conventional to pass-by-value or pass-by-reference when the method needs ownership of the value?
Why is it discouraged to accept a reference to a String (&String), Vec (&Vec), or Box (&Box) as a function argument?

answered Aug 18 '20 at 18:08

Shepmaster

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Thank you good sir. May I ask why you'd use a `Path` instead of a `PathBuf`? – robfuscator Aug 18 '20 at 21:40
1

@robfuscator that rationale is in the second “see also” link – Shepmaster Aug 18 '20 at 21:41
so what your wrote about `String` and `&str` applies for `PathBuf` and `Path` as well? – robfuscator Aug 18 '20 at 21:51

Does PathBuf::from(&some_other_pathbuf) clone the data of some_other_pathbuf?

1 Answers1