// in None case // │ in Some(_) case // ┌┴─┐ ┌───────────────────┐ if foo.map_or(true, |foo_val| foo_val < 5) { // … } For more information see Option::map_or.
If you read the documentation for Result::unwrap, you’ll note that it’s under a little section called: impl<T, E> Result<T, E> where E: Debug This means the methods in that section only exist so long as the given constraints are satisfied. The only reason unwrap wouldn’t exist is that Error doesn’t implement Debug.
Yes, crates that depend on your library will ignore your Cargo.lock. The Cargo FAQ provides more details: Why do binaries have Cargo.lock in version control, but not libraries? The purpose of a Cargo.lock is to describe the state of the world at the time of a successful build. It is then used to provide deterministic … Read more
You can use the jemalloc allocator to print the allocation statistics. For example, Cargo.toml: [package] name = “stackoverflow-30869007” version = “0.1.0” edition = “2018” [dependencies] jemallocator = “0.5” jemalloc-sys = {version = “0.5”, features = [“stats”]} libc = “0.2” src/main.rs: use libc::{c_char, c_void}; use std::ptr::{null, null_mut}; #[global_allocator] static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc; extern “C” fn … Read more
You can use serde_json::Value. #[tokio::main] async fn main() -> Result<(), Box<dyn std::error::Error>> { let resp = reqwest::get(“https://httpbin.org/ip”) .await? .json::<serde_json::Value>() .await?; println!(“{:#?}”, resp); Ok(()) } You will have to add serde_json to your Cargo.toml file. [dependencies] … serde_json = “1”
as casts are fundamentally different from From conversions. From conversions are “simple and safe” whereas as casts are purely “safe”. When considering numeric types, From conversions exist only when the output is guaranteed to be the same, i.e. there is no loss of information (no truncation or flooring or loss of precision). as casts, however, … Read more
You may want to re-read The Rust Programming Language, specifically the sections on: mutability mutable references vectors We can also iterate over mutable references to each element in a mutable vector in order to make changes to all the elements. The for loop in Listing 8-9 will add 50 to each element. let mut v … Read more
Yes, the ? operator is equivalent to try!(). ? is now in stable Rust 1.13, released on November 10, 2016. The best source of documentation at the moment seems to be RFC 0243. Note that the catch described in the RFC is not yet implemented at this writing (issue).
From the home crate. The definition of home_dir provided by the standard library is incorrect because it relies on the $HOME environment variable which has basically no meaning in Windows. This causes surprising situations where a Rust program will behave differently depending on whether it is run under a Unix emulation environment. Neither Cargo nor … Read more
You can use Vec‘s extend method. extend takes a value of any type that implements IntoIterator (which includes all iterator types) and extends the Vec by all elements returned from the iterator: vector.extend(it) Since extend belongs to the Extend trait, it also works for many other collection types.