1,574 questions
1
vote
2
answers
46
views
Comparing Swift's and Rust's function signatures
I want to check my understanding of how Swift and Rust handle function parameters.
From what I’ve seen, Swift has two main parameter modes:
Pass by value, immutable: f(x: T) and
Pass by reference, ...
- 11
4
votes
1
answer
57
views
If the return value of a function has the same lifetime as one of the arguments, then the return value is considered a borrow of the argument?
Where in Rust's specification does it say that if the returned reference of a function has the same lifetime as one of the reference arguments, then the returned reference is considered a borrow of ...
- 1,041
0
votes
0
answers
73
views
Non-bitwise move or `Move` trait? [duplicate]
In Rust, how can I define&manipulate objects that cannot be just copied bit-by-bit when they're moved?
For example, an object that contains a relative pointer (i.e. a pointer whose target is ...
- 28.7k
1
vote
0
answers
72
views
Why does the rust compiler keep a mutable reference here? [duplicate]
Consider the following program:
struct RNG {
numbers: Vec<u32>,
}
impl RNG {
pub fn new() -> RNG {
RNG { numbers: vec![] }
}
pub fn generate_random_numbers(&mut ...
- 351
1
vote
2
answers
79
views
Question about Rust bracket operator plus ampersand
The following snippet is from the (Brown University ver.) Rust book
fn largest<T>(list: &[T]) -> &T {
let mut largest = &list[0];
for item in list {
if item > ...
- 47
2
votes
2
answers
63
views
Is there a way to release and recapture references in closures while iterating?
I have code analogous to:
struct L {
length: usize,
count: usize,
}
impl L {
fn iter(&self, ns: impl Iterator<Item=usize>) -> impl Iterator<Item=usize> {
ns....
- 141
-2
votes
2
answers
109
views
Converting Option<String> to Option<&str> in match statement
I have a function that takes in a Option<&str>, but my var is currently a Result<String> that I have converted to Option<String> in a match statement.
let geom_source= std::fs::...
- 13
1
vote
1
answer
133
views
Why does this conditional assignment give a borrow error when inside a loop but not outside?
This code
// No particular meaning, just MVCE extracted from larger program
pub fn foo(mut v: Vec<i32>) {
let x = &v[0];
for _ in [0, 1] {
if *x == 0 {
v[0] = 0;
...
- 22.5k
1
vote
0
answers
99
views
Why does Miri report UB in this safe looking manual String::from_raw_parts usage after Vec::set_len(0)?
I'm experimenting with manually handling the deallocation of Strings stored in a Vec<String> by taking raw parts and calling String::from_raw_parts after setting the vec's length to 0.
The ...
- 131
2
votes
4
answers
231
views
How to define Rust HashMap where the keys are refences to the values?
I am porting some of my more complex C++ code over to Rust as a way to learn the language. One thing I have is a map of values keyed by a std::string held inside the value type, to avoid copying the ...
user4218502
3
votes
3
answers
166
views
Given a pointer x, why does setting y = x pass ownership, but y = &*x does not?
I am trying to understand the concept of ownership better. The code below does not compile:
fn main() {
let x = Box::new(1);
let y = x;
println!("{}", x);
}
This makes sense, because ...
- 31
0
votes
0
answers
39
views
Shared logic to return both a mutable and non-mutable reference in Rust [duplicate]
I'm fairly new to Rust, and this is a pattern that I've observed a few times. In the contrived example below, I have a struct with two fields of the same type: first: Vec<u32> and second: Vec<...
- 6,021
3
votes
2
answers
89
views
Insert to a HashMap if the key doesn't already exist, without cloning the key if it already exists?
I have a HashMap whose key type holds a heap allocation. I don't know if the HashMap already contains a particular key, and I would like to insert a new entry if the key doesn't already exist. How ...
- 5,770
-1
votes
1
answer
60
views
How do I move a Sender object out of a mutable reference to a Vector of tuples of Strings and Sender Objects?
This is not a solution to my problem. The suggested answer replaces the values with Nones. I quite literally require the size of my vector to reduce.
MRE:
use tokio::sync::mpsc;
#[tokio::main]
async ...
- 2,310
0
votes
1
answer
60
views
modify function to also return a mutable reference to a field of &mut self
Here is a rust function from my project
llms-client::gemini::types::Session::update()
pub(super) fn update(&mut self, reply: &str) {
let history = &mut self.history;
if ...
- 11