RefCell Smart Pointer

Exercises

Borrowing

// Complete the following code.

use std::cell::RefCell;

fn main() {
    // storing value 5 on heap
    let ptr = RefCell::new(5);
    // get an immutable reference to the stored value
    let ref1 = ;
    println!("Stored value: {}", ref1);
    drop(ref1);
    // get a mutable reference to the stored value
    let mut ref2 = ;
    *ref2 = 6; // Note: we can mutate the value associated with ptr, even though it is not marked as mut
    println!("Stored value: {}", ref2);
}

use std::cell::RefCell;

fn main() {
  // storing value 5 on heap
  let ptr = RefCell::new(5);
  // get an immutable reference to the stored value
  let ref1 = ptr.borrow();
  println!("Stored value: {}", ref1);
  drop(ref1);
  // get a mutable reference to the stored value
  let mut ref2 = ptr.borrow_mut();
  *ref2 = 6; // Note: we can mutate the value associated with ptr, even though it is not marked as mut
  println!("Stored value: {}", ref2);
}

Interior mutability

// Fix the print_details method. You can only modify the method body.

use std::cell::RefCell;

struct Student {
    name: String,
    marks: u8,
    grade: RefCell<char>,
}

impl Student {
    fn new(name: &str, marks: u8) -> Self {
        Student {
            name: name.to_owned(),
            marks,
            grade: RefCell::new('X'),
        }
    }

    fn print_details(&self) {
        let grade = match self.marks {
            0..=33 => 'C',
            34..=60 => 'B',
            _ => 'A',
        };
        self.grade = grade;
        println!(
            "name: {}, marks: {}, grade: {}",
            self.name,
            self.marks,
            self.grade.borrow()
        );
    }
}

fn main() {
    let student = Student::new("Harry", 70);
    student.print_details();
}

use std::cell::RefCell;

struct Student {
  name: String,
  marks: u8,
  grade: RefCell<char>,
}

impl Student {
  fn new(name: &str, marks: u8) -> Self {
      Student {
          name: name.to_owned(),
          marks,
          grade: RefCell::new('X'),
      }
  }

  fn print_details(&self) {
      let grade = match self.marks {
          0..=33 => 'C',
          34..=60 => 'B',
          _ => 'A',
      };
      *self.grade.borrow_mut() = grade;
      println!(
          "name: {}, marks: {}, grade: {}",
          self.name,
          self.marks,
          self.grade.borrow()
      );
  }
}

fn main() {
  let student = Student::new("Harry", 70);
  student.print_details();
}