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I've mostly only dabbled in Rust, but I recall it being really difficult to pass data by copy in Rust. It seemed to want you to pass things by reference, especi

I've mostly only dabbled in Rust, but I recall it being really difficult to pass data by copy in Rust. It seemed to want you to pass things by reference, especially if your type is meant to implement any prominent trait. It didn't matter if my type was an int, Rust seemed to want me to pass it by reference.

lukebitts 7y ago
Do you have an example? Copying is only hard to the extent that you need to #[derive(Copy)] for your type, and ints are already Copy. I also don't see how other traits factor here.
- weberc2 7y ago
  It's been a while, but I tried implementing a trait that took `&self` with several different types. One such type was an integer type, so I had to pass by reference. It's probably not a big deal, but there are many things like this that seem to prefer you move or reference rather than copy. I think it would be better for all traits to implement their methods on `self` and then the caller can choose whether the type that implements the trait is `i64` or `&i64` (instead of the trait being prescriptive about the type, which largely defeats the purpose of traits to begin with). That said, I'm not very experienced in Rust, so I expect someone can correct me about why this is a Very Bad Idea.
  - lytigas 7y ago
    Rust basically has this functionality. Whether a type is borrowed or not dictates what I can do with it. For example, I cannot remove items from a `Vec` with a shared &reference. Thus, without knowing which reference type is used in a trait method, I cannot write generic code; I don't know whether my function must take &T or T. There might be a way around this limitation, but it makes figuring out who is supposed to free a resource hard to do. The rust solution is to have different traits for different levels of ownership. For example, if I want to iterate over a vector of strings, I can get a Iterator<&str> without destroying the vector. If I'm willing to destroy it, I can get an Iterator<String>. Or, you can actually implement a trait on a reference type[0] to convert a `self` argument to effectively `&self`. This is the recommended way to implement some conversions, using AsRef and/or Into[1]. [0] https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=f7f9b2a0a956b6b6776452133f5c53fc https://play.rust-lang.org/?version=stable&mode=debug&editio... [1] https://doc.rust-lang.org/std/convert/trait.AsRef.html https://doc.rust-lang.org/std/convert/trait.AsRef.html

lukebitts 7y ago

Do you have an example? Copying is only hard to the extent that you need to #[derive(Copy)] for your type, and ints are already Copy. I also don't see how other traits factor here.

weberc2 7y ago
It's been a while, but I tried implementing a trait that took `&self` with several different types. One such type was an integer type, so I had to pass by reference. It's probably not a big deal, but there are many things like this that seem to prefer you move or reference rather than copy. I think it would be better for all traits to implement their methods on `self` and then the caller can choose whether the type that implements the trait is `i64` or `&i64` (instead of the trait being prescriptive about the type, which largely defeats the purpose of traits to begin with). That said, I'm not very experienced in Rust, so I expect someone can correct me about why this is a Very Bad Idea.
- lytigas 7y ago
  Rust basically has this functionality. Whether a type is borrowed or not dictates what I can do with it. For example, I cannot remove items from a `Vec` with a shared &reference. Thus, without knowing which reference type is used in a trait method, I cannot write generic code; I don't know whether my function must take &T or T. There might be a way around this limitation, but it makes figuring out who is supposed to free a resource hard to do. The rust solution is to have different traits for different levels of ownership. For example, if I want to iterate over a vector of strings, I can get a Iterator<&str> without destroying the vector. If I'm willing to destroy it, I can get an Iterator<String>. Or, you can actually implement a trait on a reference type[0] to convert a `self` argument to effectively `&self`. This is the recommended way to implement some conversions, using AsRef and/or Into[1]. [0] https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=f7f9b2a0a956b6b6776452133f5c53fc https://play.rust-lang.org/?version=stable&mode=debug&editio... [1] https://doc.rust-lang.org/std/convert/trait.AsRef.html https://doc.rust-lang.org/std/convert/trait.AsRef.html