What is rust cell?
In Rust document, Cell is “A mutable memory location”, and RefCell is “A mutable memory location with dynamically checked borrow rules”. Cell copies or moves contained value, while RefCell allows both mutable and immutable reference borrowing.
What is a RefCell T >`?
The RefCell type is useful when you’re sure your code follows the borrowing rules but the compiler is unable to understand and guarantee that. Similar to Rc , RefCell is only for use in single-threaded scenarios and will give you a compile-time error if you try using it in a multithreaded context.
What is a mutable reference?
A mutable reference is a borrow to any type mut T , allowing mutation of T through that reference. The below code illustrates the example of a mutable variable and then mutating its value through a mutable reference ref_i .
Is RefCell thread safe?
But then we’d have a problem: RefCell is not thread safe; it keeps track of the borrowing count using non-atomic operations. In the end, this means that you may need to pair Arc with some sort of std::sync type, usually Mutex.
What is pin in Rust?
Pin wraps a pointer and stops its value from moving. The only exception is if the value impls Unpin — then we know it’s safe to move. Voila! Now we can write self-referential structs safely! This is really important, because as discussed above, many Futures are self-referential, and we need them for async/await.
What is ref in Rust?
ref annotates pattern bindings to make them borrow rather than move. It is not a part of the pattern as far as matching is concerned: it does not affect whether a value is matched, only how it is matched.
How do you use an RC in Rust?
To enable multiple ownership, Rust has a type called Rc , which is an abbreviation for reference counting. The Rc type keeps track of the number of references to a value to determine whether or not the value is still in use.
How do you borrow on Rust?
When a function transfers its control over a variable/value to another function temporarily, for a while, it is called borrowing. This is achieved by passing a reference to the variable (& var_name) rather than passing the variable/value itself to the function.
What is Mut in Rust?
mut stands for mutable. You are telling the Rust compiler that you will be changing this variable. What’s nice is that Rust holds you to this contract. If you declare a variable using mut and never change it you’ll see this warning.
What is borrowed reference?
When a function passes ownership of a reference on to its caller, the caller is said to receive a new reference. When no ownership is transferred, the caller is said to borrow the reference.
What is unpin rust?
Trait std::marker::Unpin. Implementing the Unpin trait for T lifts the restrictions of pinning off the type, which then allows moving T out of Pin> with functions such as mem::replace . Unpin has no consequence at all for non-pinned data.
Is unpin safe?
It is only unsafe if you do impl std::marker::Unpin for InnerData {} , which promises the compiler something untrue. It won’t be able to stop you from writing Pin::new(&mut self.