Ownership semantics are a set of rules that govern the lifetime of allocated resources. Ownership semantics determine when and how allocated resources can be freed, and whether ownership can be shared.
Questions tagged [ownership-semantics]
67 questions
4
votes
1 answer
weak self be used in DispatchQueue
Here is a simple API class as shown below.
class API {
func fetchData(_ callback: @escaping (Data) -> Void) {
// reqeust to server...
callback(response)
}
}
When we call fetchData in the code below, we use [weak self] to…
user3569109
- 191
- 8
3
votes
2 answers
Why does this "cannot move out of `self.x` which is behind a mutable reference" error happen?
I'm trying to write Tetris in rust. I have structs in this project that I want to treat as immutable even though they do mutate.
The approach I'm using to achieve this kind of behavior is this:
#[derive(Debug)]
struct Example {
foo: i8
}
impl…
eliaxelang007
- 43
- 4
3
votes
2 answers
Is using std::span into an std::vector after push_back is called undefined behavior
My understanding of std::span is that it is essentially contains pointer into a container, a size, and some useful member functions.
template
class SimpleSpan {
T* ptr;
size_t length;
// some member functions
}
I can take a…
user542101
- 93
- 5
3
votes
1 answer
Mutating a struct's fields after a move
I was puzzled by the following behavior: could someone explain what is going on?
Consider the code:
struct Point {
cx : u32,
}
fn main() {
let mut p1 = Point { cx: 100 };
let p2 = p1;
p1.cx = 5000;
// println!("p1.x =…
Ranjit Jhala
- 1,242
- 8
- 18
3
votes
2 answers
Initialization and management of a shared_ptr to base interface
I have some questions related to the use of a shared_ptr pointing to a base class. Their answers influence each other, and for all three I need the same code snippet to set the context in as minimal a way as possible, like this (all the questions…
aPonza
- 492
- 4
- 10
3
votes
1 answer
Cannot move out of borrowed content on enum containing a boxed trait object when deriving PartialEq
I'm trying to write an enum deriving PartialEq which contains a trait object which does so manually. I used the solution here in order to force implementors of Trait to write an equality method. This fails to compile:
trait Trait {
fn…
Zack
- 43
- 1
- 2
3
votes
1 answer
Conditionally move T out from Rc when the count is 1
Is there a way to move an object from an Rc when the count is 1? I am thinking about how one would implement:
fn take_ownership(shared: Rc) -> Result> { ... }
The semantics would be that you get T if the count is 1 and you get…
Victor Savu
- 936
- 14
- 19
3
votes
1 answer
Is there a way to avoid cloning when converting a PathBuf to a String?
I need to simply (and dangerously - error handling omitted for brevity) get the current executable name. I made it work, but my function converts a &str to String only to call as_str() on it later for pattern matching.
fn binary_name() -> String {
…
Maciej Goszczycki
- 1,118
- 10
- 25
3
votes
1 answer
Why this function return an (owned) value?
the code
from: Genie howto repeat a string N times as an string arrayGenie howto repeat a string N times as an string array
def repeatwithsep (e: string, n: int, separator: string): string
var elen = e.length;
var slen = separator.length;
…
Naam Famas
- 124
- 7
2
votes
1 answer
vector of string slices goes out of scope but original string remains, why is checker saying there is an error?
Beginner at rust here. I understand why the code below has an error. test(x) creates y then returns a value that references the &str owned by y. y is destroyed as it goes out of scope so it can't do that.
Here's my issue the thing is the &str owned…
Brian Yeh
- 3,119
- 3
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- 40
2
votes
2 answers
Confuse about borrowing in Rust
I have 2 example code.
1st Example Code
fn main() {
let mut s = String::from("hello");
let r1 = &mut s;
let r2 = & s;
println!("{}", r2);
}
2nd Example Code
fn main() {
let mut s = String::from("hello");
let r1 = &mut…
Hello World
- 740
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- 18
2
votes
0 answers
How can I release ownership of a resource managed by a Cleaner?
Suppose I have a wrapper object like this:
private val CLEANER = java.lang.ref.Cleaner.create()
internal typealias Ptr = Long
private external fun acquireResource(): Ptr
private external fun disposeResource(nativePtr: Ptr)
/* ... */
class…
user3840170
- 26,597
- 4
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- 62
2
votes
2 answers
Ownership of global resources after fork
Consider a Foo that holds some resource
struct Foo
{
~Foo();
};
and a global std::vector. Perhaps stupid example, but it illustrates the problem well.
std::vector bar;
Now, the processes forks.
If bar is then only modified by…
user877329
- 6,717
- 8
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- 88
2
votes
1 answer
What happens when a copy of a shared pointer is created whose object contains a unique pointer?
I have been messing about with SFML, figuring out how a simple 2D game could be built. I just noticed this behaviour and couldn't figure out what's going on. Sample code for what is confusing me:
struct Unique {};
class Shared {
public:
…
karnage
- 183
- 9
2
votes
1 answer
Getting around Rust ownership problems when using state machine pattern
This question is about a specific pattern of ownership that may arise when implementing a state machine for a video game in Rust, where states can hold a reference to "global" borrowed context and where state machines own their states. I've tried to…
Guy
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