rust

问题 I´m writing a VM in Rust and I have a C and C++ background. I need union-like functionality because on the VM stack I can either store an int or a float . In C I had a union: union stack_record_t { int i; float f; }; I can use the record as int or as float with zero runtime overhead. I have a static bytecode analyzer which will find type errors before the bytecode executes, so I don't have to store a flag alongside the record. I don´t know if it is a good idea to use unions in Rust because

问题 Is there any way to achieve undefined behavior in Rust without using unsafe ? Of course, such behavior can be wrapped by a third-party library in a "safe" function so let's assume we're using only the standard one. 回答1: Absolutely, but any such case is a bug with Rust or the standard libary. My favorite example is LLVM loop optimization can make safe programs crash, which actually occurs due to a poor interaction of Rust and LLVM semantics: pub fn oops() { (|| loop { drop(42) })() } Compiled

问题 What's the best way to read from a type implementing the std::io::Read trait when the contents of the output isn't important? Possible options I see are: Read single bytes in a loop. Allocate a potentially huge vector and read into that. Something in-between... read into a fixed sized buffer in a loop . The first 2 options don't seem ideal, the third is OK but inconvenient. Does Rust provide a convenient way to achieve this? 回答1: You can use io::copy(), Read::take() and io::sink() to discard

问题 I've very recently started studying Rust, and while working on a test program, I wrote this method: pub fn add_transition(&mut self, start_state: u32, end_state: u32) -> Result<bool, std::io::Error> { let mut m: Vec<Page>; let pages: &mut Vec<Page> = match self.page_cache.get_mut(&start_state) { Some(p) => p, None => { m = self.index.get_pages(start_state, &self.file)?; &mut m } }; // omitted code that mutates pages // ... Ok(true) } it does work as expected, but I'm not convinced about the m

问题 What's the best way to read from a type implementing the std::io::Read trait when the contents of the output isn't important? Possible options I see are: Read single bytes in a loop. Allocate a potentially huge vector and read into that. Something in-between... read into a fixed sized buffer in a loop . The first 2 options don't seem ideal, the third is OK but inconvenient. Does Rust provide a convenient way to achieve this? 回答1: You can use io::copy(), Read::take() and io::sink() to discard

问题 I am attempting to set up a project very similar to dueboot. That is, Rust on embedded ARM. Right now, I'm only up to the point of compiling the Rust code, but I can't get it to compile. I've basically copied the rust code exactly from that project, but I don't fully understand the lang_items feature. #![feature(asm)] #![feature(lang_items)] #![feature(no_std)] #![no_std] use arduino::{init, delay, pinMode, digitalWrite, analogWrite, LOW, HIGH, OUTPUT}; mod arduino; #[lang="sized"] trait

问题 I need to check if all items are unique in an array of serde_json::Value . Since this type does not implement Hash I came up with the following solution: use serde_json::{json, Value}; use std::collections::HashSet; fn is_unique(items: &[Value]) -> bool { let mut seen = HashSet::with_capacity(items.len()); for item in items.iter() { if !seen.insert(item.to_string()) { return false; } } true } fn main() { let value1 = json!([1, 2]); assert!(is_unique(&value1.as_array().unwrap())); let value2 =

问题 I am trying to use the following Rust code to connect to EC2 instances. #[test] fn client_ssh_timeout2() { match Command::new("/usr/bin/ssh -i /tmp/.ssh/25.pem ubuntu@ip").spawn() { Ok(_) => println!("Able to ssh"), Err(e) => println!("{:?}", e), }; } But I am getting the following error Error { repr: Os { code: 2, message: "No such file or directory" } } Has anyone been able to use std::process::Command or any other Rust library to connect to EC2 instances using PEM files? I tried using ssh2

问题 I have a struct like this: #[derive(Serialize, Deserialize)] struct Thing { pub small_header: Header, pub big_body: Body, } I want to serialize this Thing to send over the network. I already have a Body available but I can't move it (imagine I am doing something with it, and every now and then I receive a command to temporarily stop what I'm doing and send over whatever data I have now) and I can't copy it (it's too big, possibly hundreds of megabytes). So I'd like Serde to just borrow the

问题 I'm new to Rust and have seen some examples of people using Box to allow pushing many types that implement a certain Trait onto a Vec. When using a Trait with Generics, I have run into an issue. error[E0038]: the trait `collision::collision_detection::Collidable` cannot be made into an object --> src/collision/collision_detection.rs:19:5 | 19 | collidables: Vec<Box<Collidable<P, M>>>, | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `collision::collision_detection::Collidable`