How do I return a reference to something inside a RefCell without breaking encapsulation?

by

You can create a new struct similar to the Ref<'a,T> guard returned by RefCell::borrow(), in order to wrap this Ref and avoid having it going out of scope, like this:

use std::cell::Ref;

struct FooGuard<'a> {
    guard: Ref<'a, MutableInterior>,
}

then, you can implement the Deref trait for it, so that it can be used as if it was a &Vec<i32>:

use std::ops::Deref;

impl<'b> Deref for FooGuard<'b> {
    type Target = Vec<i32>;

    fn deref(&self) -> &Vec<i32> {
        &self.guard.vec
    }
}

after that, update your get_items() method to return a FooGuard instance:

impl Foo {
    pub fn get_items(&self) -> FooGuard {
        FooGuard {
            guard: self.interior.borrow(),
        }
    }
}

and Deref does the magic:

fn main() {
    let f = Foo {
        interior: RefCell::new(MutableInterior {
            vec: Vec::new(),
            hide_me: 2,
        }),
    };
    let borrowed_f = &f;
    let items = borrowed_f.get_items();
    let v: &Vec<i32> = &items;
}

More Related Contents:

  1. Mutably borrow one struct field while borrowing another in a closure
  2. Situations where Cell or RefCell is the best choice
  3. How do I borrow a RefCell, find a key, and return a reference to the result? [duplicate]
  4. How to use struct self in member method closure
  5. cannot borrow `self.x` as immutable because `*self` is also borrowed as mutable
  6. How can I modify self in a closure called from a member function?
  7. How does the Rust compiler know `Cell` has internal mutability?
  8. What is the difference between iter and into_iter?
  9. How does for syntax differ from a regular lifetime bound?
  10. How to get a reference to a concrete type from a trait object?
  11. How can I create my own data structure with an iterator that returns mutable references?
  12. How do I convert a Rust closure to a C-style callback?
  13. How to transform fields during serialization using Serde?
  14. Why is the mutable reference not moved here?
  15. How do I use static lifetimes with threads?
  16. Is it possible to conditionally enable an attribute like `derive`?
  17. How can I create a function with a variable number of arguments?
  18. How do I fix “cannot find derive macro in this scope”?
  19. Why is the bound `T: ‘a` required in order to store a reference `&’a T`?
  20. Type mismatches resolving a closure that takes arguments by reference
  21. How do I disambiguate traits in Rust?
  22. How do I change a function’s qualifiers via conditional compilation?
  23. Creating a vector of zeros for a specific size
  24. What is the difference between immutable and const variables in Rust?
  25. What is the purpose of the unit type in Rust?
  26. How to iterate through a Hashmap, print the key/value and remove the value in Rust?
  27. Why does the Rust compiler request I constrain a generic type parameter’s lifetime (error E0309)?
  28. Cannot pass self as callback parameter due to double borrowing
  29. How to print structs and arrays?
  30. Can Rust optimise away the bit-wise copy during move of an object someday?

Leave a Comment