That’s simply the way it is. In Rust a trait must be in scope for you to be able to call its methods. As for why, the possibility of collisions is the reason why. All the formatting traits in std::fmt (Display, Debug, LowerHex, &c.) have the same method signature for fmt. For example; what would …
Rust 1.51 Use const generics: struct Vec<T: Sized, const COUNT: usize> { a: [T; COUNT], } Previous versions RFC 2000 — const generics introduces support for this and progress is tracked in issue #44580. If you look at the design of Rust, you will notice that it started first by tackling the hardest problems (memory-safe, …
In cases like this, it’s very useful to force the compiler to tell you the type of the variable. Let’s trigger a type error by assigning the closure argument to an incompatible type: array_iter.filter(|x| { let _: () = x; x == 2 }); This fails with: error[E0308]: mismatched types –> src/lib.rs:4:41 | 4 | …
Standard library futures Let’s use this as our minimal, reproducible example: async fn example() -> i32 { 42 } Call executor::block_on: use futures::executor; // 0.3.1 fn main() { let v = executor::block_on(example()); println!(“{}”, v); } Tokio Use the tokio::main attribute on any function (not just main!) to convert it from an asynchronous function to a …
Just use Duration and appropriate operator: use chrono::{Duration, Utc}; fn main() { let dt = Utc::now() + Duration::days(137); println!(“today date + 137 days {}”, dt); } Test on playground.
The command line solution may help you to configure your IDE: cargo +nightly test Provided, of course, that you have the nightly channel installed. If not, perhaps install it with rustup install nightly (no need to switch to it, but check you’re still on stable: rustup show).
As of Rust 1.21.0, Vec::splice is available and allows inserting at any point, including fully prepending: let mut vec = vec![1, 5]; let slice = &[2, 3, 4]; vec.splice(1..1, slice.iter().cloned()); println!(“{:?}”, vec); // [1, 2, 3, 4, 5] The docs state: Note 4: This is optimal if: The tail (elements in the vector after range) …
Just replace #[test] with #[tokio::test] before any test function. If you use actix-web you can add actix_rt into Cargo.toml and #[actix_rt::test] before the test function #[tokio::test] async fn test_something_async() { let DB = setup().await; // <- the DB is impl std::future::Future type // the DB variable will be used to run another // async function …
As of Rust 1.26, you can use impl trait: fn make_adder(a: i32) -> impl Fn(i32) -> i32 { move |b| a + b } fn main() { println!(“{}”, make_adder(1)(2)); } This allows returning an unboxed closure even though it is impossible to specify the exact type of the closure. This will not help you if …
Monomorphization costs. write(), like most filesystem functions in Rust, takes AsRef<Path> instead of Path, for convenience (to allow you to pass e.g. a &str). But that also has a cost: it means that the function will be monomorphized and optimized separately for each type, while there is no real need for that. While it is …