TL;DR: One can instead use &str, &[T] or &T to allow for more generic code. One of the main reasons to use a String or a Vec is because they allow increasing or decreasing the capacity. However, when you accept an immutable reference, you cannot use any of those interesting methods on the Vec or … Read more
You want to use the buffered reader, BufRead, and specifically the function BufReader.lines(): use std::fs::File; use std::io::{self, prelude::*, BufReader}; fn main() -> io::Result<()> { let file = File::open(“foo.txt”)?; let reader = BufReader::new(file); for line in reader.lines() { println!(“{}”, line?); } Ok(()) } Note that you are not returned the linefeed, as said in the documentation. … Read more
According to the example from the std::fmt docs: extern crate uuid; use uuid::Uuid; use std::fmt; struct BlahLF { id: Uuid, } impl fmt::Debug for BlahLF { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, “Hi: {}”, self.id) } } The part to emphasize is the fmt:: in fmt::Result. Without that you’re referring to the … Read more
Since Rust 1.19, you can statically link the C runtime (CRT) to avoid this very common situation on Windows: The program can’t start because VCRUNTIME140.dll is missing from your computer. Try reinstalling the program to fix this problem. Add this to your .cargo/config file, using the appropriate target triple for your platform: [target.x86_64-pc-windows-msvc] rustflags = … Read more
Cargo passes some metadata to the compiler through environment variables, a list of which can be found in the Cargo documentation pages. The compiler environment is populated by fill_env in Cargo’s code. This code has become more complex since earlier versions, and the entire list of variables is no longer obvious from it because it … Read more
Your code is invalid because you try to return multiple mutable references to the same slice with the same lifetime ‘a. For such a thing to work, you would need a different lifetime for each returned Item so that you wouldn’t hold 2 mutable references to the same slice. You cannot do that for now … Read more
Why does this particular example not work? The chapter Trait Objects states: So what makes a method object-safe? Each method must require that Self: Sized Isn’t that fulfilled? This question really is: What is a trait object? A trait object is an interface in the Object-Oriented paradigm: it exposes a limited set of methods, which … Read more
Let’s look at Connection::prepare: pub fn prepare<‘a>(&’a self, sql: &str) -> Result<Statement<‘a>> If we ignore the Result (which just means that this function can fail), this means “return a Statement that can live no longer than the Connection that prepare was called on”. This is likely due to the Statement containing a reference to the … Read more
A really common pitfall in C++ programs, and even in Java programs, is modifying a collection while iterating over it, like this: for (it: collection) { if (predicate(*it)) { collection.remove(it); } } For C++ standard library collections, this causes undefined behaviour. Maybe the iteration will work until you get to the last entry, but the … Read more
It has several uses. It can be used for functions which are designed to panic or exit the program. panic!() itself is one such function, but it can also be applied to functions which wrap panic!(), such as printing out more detailed error information and then panicking. It can also be used for functions that … Read more