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
The other answers are outdated. As of Rust 1.27, you can use HashMap::retain to keep only the elements you are interested in. You specify the elements to keep using a closure. x.retain(|_, v| *v != 0);
It is definitely an interesting one. They are similar – but not quite the same. resize() is a member of Vec. rotate_right(), on the other hand, is a method of slices. Vec<T> derefs to [T], so most of the time this does not matter. But actually, while this call: vec.resize(vec.len(), 0); Desugars to something like: … Read more
This one seems convoluted at first, but remember that String and &str are different beasts. String can live and be used on its own, but &str is just a reference to part of String. So, &str can live as long as referenced String lives. Lets see how it should work on return signatures. let title_text … Read more
This is a known issue that will be solved by a future iteration of non-lexical lifetimes, but is not currently handled as of Rust 1.57. If you are inserting to the same key that you are looking up, I’d encourage you to use the entry API instead. You can add a smidgen of inefficiency to … Read more
You are completely right with both your reasoning and your observations. It definitely looks like things should be happening the way you describe it. However, the compiler applies some convenience magic here. Move semantics generally apply in Rust for all types that do not implement the Copy trait. Shared references are Copy, so they are … Read more
In your example, [1, 2, 3] is not treated as local variable, but as static one! Let’s take a look at this code: fn foo() -> &’static [i32] { &[1, 2, 3] } This works! Some time ago, RFC 1414: Rvalue Static Promotion was merged: “Promote constexpr rvalues to values in static memory instead of … Read more
Let’s look at the signature for into_bytes: fn into_bytes(self) -> Vec<u8> This takes self, not a reference to self (&self). That means that self will be consumed and won’t be available after the call. In its place, you get a Vec<u8>. The prefix into_ is a common way of denoting methods like this. I don’t … Read more
Let’s look at a simple implementation of this: struct Parent { count: u32, } struct Child<‘a> { parent: &’a Parent, } struct Combined<‘a> { parent: Parent, child: Child<‘a>, } impl<‘a> Combined<‘a> { fn new() -> Self { let parent = Parent { count: 42 }; let child = Child { parent: &parent }; Combined { … Read more