20 Mar 2026

Day 4 of 100 Days Rusty

what i learnt in Rust today

Reference and borrowing

reference is basically pointer to a variable, below example shows the usage

fn main() {
    let mut s = String::from("Hello");
    push_world(&mut s);
    println!("{s}")
}

fn push_world(s: &mut String) {
    s.push_str("world")
}

Rules of referencing a borrow

at any given time, you can exactly one mutable reference and any number of immutable reference
reference are always valid in rust

In rust you can not create a dangling reference (i.e; null pointer):

fn main() {
    let str = dangle(); // This will not compile,
}

fn dangle() -> &String {
    let s = String::from("dangle");     // create a string
    return &s;  //returning reference to it
} // here s is dropped as it goes out of scope, therefore creating a dangling reference
// but rust will not compile this, therefore the property, **references are always valid**