The rule of thumb I always tell people is that they should generally put owned data into struct fields and references into function parameters.
this post was submitted on 31 Jan 2026
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Good rule of thumb. As long as it's not followed blindly of course.
Structs with lifetimes are often quite convenient. Especially for performance.
I recently learned you can pass a &String to a &str parameter, so that's neat.
Ah yeah, via deref coercion, which is also called "auto-dereferencing" at times. Not to be confused with "auto-referencing", which is also a thing^1.
You can do some wild shit with deref coercion. And when I say "wild", I guess, I'm talking about the most normal thing for Java devs, because well, it's a lot like inheritance. 😅
Basically, this concept of being able to pass &String into a parameter that takes &str also applies to the self parameter. Or in other words, methods implemented on str can also be called on String, as if String extends str.
And well, obviously you can also make use of that yourself, by writing your own wrapper type. You can even "override" existing methods in a sense by re-defining them in the wrapper type.
I had to play around a bit with it myself, so here's a playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=af65ed396dec88c8406163acaa1f8f8d
Welp, I posted my hot take that impl Deref is similar to inheritance as a meme in !rust@lemmy.ml: https://lemmy.ml/post/42514248
Now, let's see how many feathers get ruffled. 🙃
I like this rule of thumb and it goes nicely with the “if you have more than 3 arguments to a function, consider making a struct to pass the arguments in” rule of thumb because
You can have the struct use a named lifetime (or several) for the different parameters so it doesn’t own them!
Best of both worlds.
That's how the C++ code should have looked all the time. And the amount of people that get surprised and complain about this is just more evidence that nobody should write C++. Ever.
Exactly, C++ is what came to my mind when I saw this. Some people don't put references??
I guess, if you come from garbage-collected languages, you might be used to not needing the ampersands, because everything is automatically a reference in those...
Yeah this is how it was for me when I first started C++, I was use to any object beyond a simple 3D vector to always be passed by reference
And then I read a C++ book my uncle gave me during a flight and realized that there isn't any syntax for passing a parameter by copy, so obviously that'd have to be the default behavior and I've been passing by reference ever since
Oh wow, what the hell. I'm not actually familiar with C++ (just with Rust which gets similar reactions with the ampersands), but that's insane that it just copies shit by default. I guess, it comes from a time when people mostly passed primitive data types around the place. But yeah, you won't even notice that you're copying everything, if it just does it automatically.
And by the way, Rust did come up with a third meaning for passing non-references: It transfers the ownership of the object, meaning no copy is made and instead, the object is not anymore allowed to be used in the scope that passed it on.
That's true, except for data types which implement the Copy trait/interface, which is implemented mostly for primitive data types, which do then get treated like C++ apparently treats everything.
It probably comes from C, which also copies by default, though it doesn't have copy constructors.
There are also the move semantics in C++, which are similar to Rust's ownership transfer, but explicit and with some differences in how the data is actually handled under the hood
you got a & yes, but what about a getting more & on top of your &'s?
Hey I get that reference!
who turned excel into a programming language?
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