lifetime Questions
3
Solved
Given the following struct and impl:
use std::slice::Iter;
use std::cell::RefCell;
struct Foo {
bar: RefCell<Vec<u32>>,
}
impl Foo {
pub fn iter(&self) -> Iter<u32> {
...
1
Solved
The following code produces the lifetime errors below despite the fact that the V instance in question is owned.
use std::collections::hash_map::HashMap;
use std::cmp::Eq;
use std::hash::Hash;
tra...
1
This is my first project in Rust, and I think I'm missing something simple.
I'm attempting to create a simple Web API daemon that will receive POSTs of JSON, parse the JSON, and send an email usi...
Allpowerful asked 24/11, 2019 at 1:36
7
Solved
How to set session lifetime in PHP? I Want to set it to forever as long as the request is exist. The request is AJAX. My PHP code that handle AJAX request is:
// AJAX.php
<?php
session_start(...
2
Solved
Actually I started with Blazor and EF Core. At registering the DbContext i get stucked. The DbContext can be registerd with AddDbContext or with AddDbContextFactory. But what´s the difference?
buil...
Lamellirostral asked 6/12, 2021 at 14:39
2
I've been trying to find a good explanation of Rust lifetimes. I get the idea that they are our way of telling the compiler which variables have to outlive which, so it can verify that references a...
2
Solved
I'm still trying to understand Rust ownership and lifetimes, and I'm confused by this piece of code:
struct Foo {
x: String,
}
fn get_x<'a, 'b>(a: &'a Foo, b: &'b Foo) -> &'b...
1
I am attempting to define a struct, in Rust, that contains a member of type async_executor::LocalExecutor, a type that, itself, is generic over a lifetime, 'a:
pub struct LocalExecutor<'a> {
...
3
Solved
I am in the process of learning Rust and was testing some array copying through a function. I am sure there are built-in Rust functions to copy/clone array information, but a personal implementatio...
2
Solved
I'm trying to learn Rust's ownership and lifetimes in more detail, and I'm very confused by this piece of code:
let mut lst = vec![1, 2, 3];
let mut x = &mut 0;
for value in &mut lst {
*v...
1
Solved
I think my question relates to Rust Issue 57017.
The following code does not compile and produces error: future cannot be sent between threads safely due to future created by async block is not 'Se...
Guess asked 30/9, 2021 at 11:54
7
I've tried to code like this several times:
struct Foo
{
double const& f;
Foo(double const& fx) : f(fx)
{
printf("%f %f\n", fx, this->f); // 125 125
}
double GetF() const
{
ret...
1
Solved
Consider this snippet:
#include <iostream>
#include <string>
#include <string_view>
using namespace std::literals;
class A
{
public:
std::string to_string() const noexcept
{
...
Concurrent asked 23/8, 2021 at 13:26
1
Solved
Put it other way, conversely, are std::span iterators invalidated after the span instance is destroyed?
I have a vector I need to iterate over with different layouts. I'm trying to make use of std:...
1
Solved
I have the following code
use std::future::Future;
fn main() {
handle(Test::my_func);
}
fn handle<Fut>(fun: for<'r> fn(&'r mut Test) -> Fut) -> bool
where
Fut: Future<Ou...
Plaza asked 9/8, 2021 at 6:36
3
Solved
Does having a reference &'a T immediately cause UB (undefined behavior) if 'a is larger than the referenced value? OR is it fine to have such a reference as long as it does not outlive the refe...
1
Solved
I would like to return a reference to an owned object that is in a collection (viz., a Vec), but I cannot seem to get the lifetimes correct. Here is what I first tried:
struct StringHolder {
strin...
4
Solved
In a project where custom Serde (1.0) serialization and deserialization methods are involved, I have relied on this test routine to check whether serializing an object and back would yield an equiv...
Aegrotat asked 1/10, 2017 at 16:12
1
I want the async block in the following code to implement Send (Playground):
use std::collections::BTreeSet;
use std::future::ready;
pub fn test<T: Sync>(set: &BTreeSet<T>) -> i...
Karylkarylin asked 8/7, 2021 at 8:20
4
Solved
I am having trouble expressing the lifetime of the return value of an Iterator implementation. How can I compile this code without changing the return value of the iterator? I'd like it to return a...
1
Solved
I'm trying to write a constructor function which takes a generic value implementing some trait by argument, and then boxes it (the point is to then initialize something with these boxes, but the fo...
5
Solved
Rust disallows this kind of code because it is unsafe:
fn main() {
let mut i = 42;
let ref_to_i_1 = unsafe { &mut *(&mut i as *mut i32) };
let ref_to_i_2 = unsafe { &mut *(&mut ...
Fenella asked 8/3, 2018 at 13:44
2
Solved
In the following piece of code, I am trying to understand how the generic lifetime parameter 'a is specialized.
struct Wrapper<'a>(&'a i32);
fn foo() {
let mut r;
{
let x = 0; // the...
0
I am trying to pass a closure returning Future<Output=bool> to an async function and call this closure as an async predicate (something like an async .filter or other higher-order function).
...
Ewald asked 17/5, 2021 at 12:20
0
This code compiles:
async fn foo(_: impl Iterator<Item = &u32>) {}
However, removing the async, it does not work anymore:
fn foo(_: impl Iterator<Item = &u32>) {}
Instead, it ...
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