rust

问题 Example code： fn main() { let a = [1, 2, 3, 4, 5]; reset(a); } fn reset(mut b: [u32; 5]) { b[0] = 5; } The variable a is an immutable array, and the reset function's parameter b is a mutable array; intuitively I need to modify a to a mutable array before I can call the reset method, but the compiler tells me that I don't need to do this, why is this? fn main() { let mut a = [1, 2, 3, 4, 5]; reset(a); } fn reset(mut b: [u32; 5]) { b[0] = 5; } warning: variable does not need to be mutable -->

问题 I have the following code but when I start the app it requests the page but gets no answer. use std::io::Read; use std::io::Result; use std::io::Write; use std::net::TcpStream; fn main() { if let Err(err) = connect() { println!("err = {}", err); } } fn connect() -> Result<()> { let mut stream = TcpStream::connect("www.google.de:80")?; let mut request_data = String::new(); request_data.push_str("GET / HTTP/1.1"); request_data.push_str("\r\n"); request_data.push_str("Host: www.google.de");

问题 I'm trying to understand how to use the question mark operator for error handling in Rust. I have this code: fn main() -> Result<(), &'static str> { let foo: i32 = Some("1") .ok_or(Err("error 1"))? .parse() .or(Err("error 2"))?; Ok(()) } This code can not be compiled for some reason: error[E0277]: the trait bound `&str: std::convert::From<std::result::Result<_, &str>>` is not satisfied --> src/main.rs:2:20 | 2 | let foo: i32 = Some("1") | ____________________^ 3 | | .ok_or(Err("error 1"))? |

问题 I'm trying to understand how to use the question mark operator for error handling in Rust. I have this code: fn main() -> Result<(), &'static str> { let foo: i32 = Some("1") .ok_or(Err("error 1"))? .parse() .or(Err("error 2"))?; Ok(()) } This code can not be compiled for some reason: error[E0277]: the trait bound `&str: std::convert::From<std::result::Result<_, &str>>` is not satisfied --> src/main.rs:2:20 | 2 | let foo: i32 = Some("1") | ____________________^ 3 | | .ok_or(Err("error 1"))? |

问题 I'm creating a simple HTTP server. I need to read the requested image and send it to browser. I'm using this code: fn read_file(mut file_name: String) -> String { file_name = file_name.replace("/", ""); if file_name.is_empty() { file_name = String::from("index.html"); } let path = Path::new(&file_name); if !path.exists() { return String::from("Not Found!"); } let mut file_content = String::new(); let mut file = File::open(&file_name).expect("Unable to open file"); let res = match file.read_to

问题 I'm creating a simple HTTP server. I need to read the requested image and send it to browser. I'm using this code: fn read_file(mut file_name: String) -> String { file_name = file_name.replace("/", ""); if file_name.is_empty() { file_name = String::from("index.html"); } let path = Path::new(&file_name); if !path.exists() { return String::from("Not Found!"); } let mut file_content = String::new(); let mut file = File::open(&file_name).expect("Unable to open file"); let res = match file.read_to

问题 I'm writing a library in Rust that has a C interface. C side must be able to create and destroy Rust objects (C side owns them and controls their lifetime). I've managed to "leak" an object to C, but I'm not sure how to properly free it: pub extern "C" fn create() -> *mut Foo { let obj = Foo; // oops, a bug let ptr = std::mem::transmute(&mut obj); // bad std::mem::forget(obj); // not needed return ptr; } pub extern "C" fn destroy(handle: *mut Foo) { // get Foo back and Drop it??? } I'm not

问题 I'm writing a library in Rust that has a C interface. C side must be able to create and destroy Rust objects (C side owns them and controls their lifetime). I've managed to "leak" an object to C, but I'm not sure how to properly free it: pub extern "C" fn create() -> *mut Foo { let obj = Foo; // oops, a bug let ptr = std::mem::transmute(&mut obj); // bad std::mem::forget(obj); // not needed return ptr; } pub extern "C" fn destroy(handle: *mut Foo) { // get Foo back and Drop it??? } I'm not

问题 I'm writing a library in Rust that has a C interface. C side must be able to create and destroy Rust objects (C side owns them and controls their lifetime). I've managed to "leak" an object to C, but I'm not sure how to properly free it: pub extern "C" fn create() -> *mut Foo { let obj = Foo; // oops, a bug let ptr = std::mem::transmute(&mut obj); // bad std::mem::forget(obj); // not needed return ptr; } pub extern "C" fn destroy(handle: *mut Foo) { // get Foo back and Drop it??? } I'm not

问题 Assuming I wanted to (ab)use cache coherency to do lock free reads like FaRM, would it be enough to have a struct with a single 64 byte array as data to guarantee that on an architecture with 64 byte cache lines each struct would occupy exactly one cache line? 回答1: No, that wouldn't guarantee that the alignment was a cache line. RFC 1358 added the concept of #[repr(align)] , allowing the programmer to specify alignment requirements. This attribute was stabilized in Rust 1.25. For your