The code above doesn’t work, and understandibly so, moving the value out of self breaks the integrity of it. This is not exactly what happens here. For example, same thing with self would work nicely: impl<T> Foo<T> { fn switch(self) { self = match self { Foo::Bar(val) => Foo::Baz(val), Foo::Baz(val) => Foo::Bar(val), } } } … Read more
The compiler is right to prevent you from borrowing the HashMap twice. Suppose in handle_user_data() you also tried to borrow self.users. You would break the rules of borrowing in Rust because you already have a mutable borrow on it and you can only have one. Since you can’t borrow self twice for your handle_user_data(), I … Read more
Option::unwrap() consumes the option, that is, it accepts the option by value. However, you don’t have a value, you only have a reference to it. That’s what the error is about. Your code should idiomatically be written like this: fn my_fn(arg1: &Option<Box<i32>>) -> i32 { match arg1 { Some(b) => **b, None => 0, } … 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
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 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