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What is Rust Borrowing?

What is Rust Borrowing?

What is Rust Borrowing?

Borrowing

We call having references as function parameters borrowing. As in real world , if an individual owns something, we'll borrow it from them. Whenever we’re done, we've got to offer it back.

Referencing 

The reference is that the act of consulting somebody or something so as to urge information

We would declare reference in terms of Rust programing as if we are taking a replica of it without damaging or taking its ownership.


‘&’ symbol is employed to pass the reference

Have a look that how ‘&’ symbol is employed in code.

fn main() {
let s1 = String::from("hello");
let len = calculate_length(&s1);
println!("The length of {} is {}.", s1, len);
}
fn calculate_length(s: &String) -> usize {
s.len()}

Mutable References

  • The actual concept of mutable reference is same as we use mutable variable
  • When we need to modify mutable reference is employed once  the worth we make regard to.   
  • There would be “mut” keyword with the reference too because the variable or type we are making reference.
fn main() {
let s = String::from("hello");
change(&s);}
change(some_string: &String) {
some_string.push_str(", world");
}
  • If we took to start this code, we'll get a mistake because references are immutable by default in Rust.
fn main() {
let mut s = String::from("hello");
change(& mut s); }
fn change(some_string: & mut String) {
some_string.push_str(", world");
}

Restriction!

  • Mutable References have one lengthy restriction.We can have just one mutable regard to a specific piece of knowledge during a particular scope.
For Example:
let mut s = String::from("hello");
let r1 = &mut s;
let r2 = &mut s;
println!("{}, {}", r1, r2);
This is not allowed. Duplicate

Restriction Benefit
  • The benefit of having this restriction is that Rust can prevent Data Race at compile time.

Data Race Occurs when,

  • An equivalent data has access for two or more pointers at an equivalent time.
  • One among the pointers at least is getting used to write down to the information.
  • To the information there’s no mechanism getting used to synchronize access.
fn main() {
let mut s = String::from("hello");
{
let r1 = &mut s;
}
We will make a replacement reference with no problems as r1 goes out of scope here
let r2 = &mut s;
}

fn main() {
let mut s = String::from("hello");
let r1 = &s; no problem
let r2 = &s; no problem
let r3 = &mut s; BIG PROBLEM

println!("{}, {}, and {}", r1, r2, r3);
}

Data Race

  • Data races is the reason to undefined behavior and may be difficult to diagnose and fix when you’re trying to trace them down at runtime; Rust restrict this problem from doing because it won’t even compile code with data races!

Dangling Reference

  • The references of Dangling point a location in memory which will are given to somebody else . The compiler will make sure that the info won't leave of scope before the regard to the info does in Rust.

fn main() {
let reference_to_nothing = dangle();
}
fn dangle() -> &String {
let s = String::from("hello");
&s
}

error[E0106]: missing lifetime specifier
--> main.rs:5:16
|
5 | fn dangle() -> &String {
|
^ expected lifetime parameter
|
= help: this function's return type contains a
borrowed value, but there is
no value for it to be borrowed from
= help: consider giving it a 'static lifetime 

fn dangle() -> &String {
let s = String::from("hello");
&s
}
s is a new String
we return a reference to the String, s
 s here went out of scope, and is dropped. Its
memory goes away. Danger!

fn dangle() -> String {
let s = String::from("hello");
s
}

Rules of Reference

  • There may be one mutable reference or any number of immutable references.
  • References should be valid.

Summary

  • Ownership and borrowing make sure memory safety at compile time.
  • Control over your memory usage within the same way as other systems programming languages.
  • That data automatically pack up when the owner goes out of scope.
  • No extra code to urge this control.



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