rust

问题 Is there any way to accomplish something like the following: let v = vec![1, 2, 3]; let (a, b) = v.iter().take(2); Such that a = 1 and b = 2 at the end? I know I could just use a vector but I would like to have named variables. 回答1: This may not be exactly what you asked for, but I suppose you rarely want to convert an arbitrarily large vector to a tuple anyway. If you just want to extract the first few elements of a vector into a tuple, you can do so using slice pattern matching : fn main()

问题 I have the below Rust program. fn main() { let v = vec![100, 32, 57]; for i in v { println!("{}", i); } println!("{:?}", v); } When I run it, I get: error[E0382]: borrow of moved value: `v` --> src\main.rs:7:22 | 2 | let v = vec![100, 32, 57]; | - move occurs because `v` has type `std::vec::Vec<i32>`, which does not implement the `Copy` trait 3 | for i in v { | - | | | value moved here | help: consider borrowing to avoid moving into the for loop: `&v` ... 7 | println!("{:?}", v); | ^ value

问题 I have the below Rust program. fn main() { let v = vec![100, 32, 57]; for i in v { println!("{}", i); } println!("{:?}", v); } When I run it, I get: error[E0382]: borrow of moved value: `v` --> src\main.rs:7:22 | 2 | let v = vec![100, 32, 57]; | - move occurs because `v` has type `std::vec::Vec<i32>`, which does not implement the `Copy` trait 3 | for i in v { | - | | | value moved here | help: consider borrowing to avoid moving into the for loop: `&v` ... 7 | println!("{:?}", v); | ^ value

问题 Background: I'm writing a RDBMS in rust The db.catalog maintain a hashmap from table_id to table: pub struct Catalog { table_id_table_map: HashMap<i32, Box<dyn Table>>, } And when I add a boxed table to the catalog, move occurred. Then I can't use table instance anymore: // create table let table = create_random_heap_table(....); // add to catalog db.get_catalog().add_table(Box::new(table), "heap table", ""); // access table instance let table_id = table.get_id(); compile error: error[E0382]:

问题 I am trying to build a logger based on a rolling policy. Below is the closest I was able to implement: let logfile = FileAppender::builder() .encoder(Box::new(PatternEncoder::new("{d} {l}::{m}{n}"))) .build("log/output.log")?; let config = Config::builder() .appender(Appender::builder().build("logfile", Box::new(logfile))) .build(Root::builder() .appender("logfile") .build(LevelFilter::Debug))?; log4rs::init_config(config)?; This helped me log messages at all levels. However, logging to a

问题 I am trying to build a logger based on a rolling policy. Below is the closest I was able to implement: let logfile = FileAppender::builder() .encoder(Box::new(PatternEncoder::new("{d} {l}::{m}{n}"))) .build("log/output.log")?; let config = Config::builder() .appender(Appender::builder().build("logfile", Box::new(logfile))) .build(Root::builder() .appender("logfile") .build(LevelFilter::Debug))?; log4rs::init_config(config)?; This helped me log messages at all levels. However, logging to a

问题 This question already has answers here : Lifetime error when creating a function that returns a value implementing serde::Deserialize (2 answers) Closed 4 months ago . I have a simple function that I want to make generic, in rust. I am getting a lifetime error. I am still getting the hang of the lifetime side of rust. The function simply converts 1 struct into another using serde's serialization. Here is a a rust playground with the full simple scenario. Code: pub fn convert<'de: 'a, 'a, T>

问题 This question already has answers here : Lifetime error when creating a function that returns a value implementing serde::Deserialize (2 answers) Closed 4 months ago . I have a simple function that I want to make generic, in rust. I am getting a lifetime error. I am still getting the hang of the lifetime side of rust. The function simply converts 1 struct into another using serde's serialization. Here is a a rust playground with the full simple scenario. Code: pub fn convert<'de: 'a, 'a, T>

问题 This question already has answers here : Lifetime error when creating a function that returns a value implementing serde::Deserialize (2 answers) Closed 4 months ago . I have a simple function that I want to make generic, in rust. I am getting a lifetime error. I am still getting the hang of the lifetime side of rust. The function simply converts 1 struct into another using serde's serialization. Here is a a rust playground with the full simple scenario. Code: pub fn convert<'de: 'a, 'a, T>

问题 This question already has answers here : How to create a String directly? (3 answers) What is the difference between these 3 ways of declaring a string in Rust? (1 answer) Closed last month . How does String::from("") & "".to_string() differ in Rust? Is there any difference in stack and heap allocation in both cases? 回答1: How does String::from("") & "".to_string() differ in Rust? They're part of different protocols (traits): std::convert::From and alloc::string::ToString[0]. However, when it