```rust
fn main() {
    let s1 = String::from("hello");

    // Pass an immutable reference to the function
    let len = calculate_length(&s1);

    println!("The length of '{}' is {}.", s1, len);
}

fn calculate_length(s: &String) -> usize {
    s.len()
}
// s goes out of scope, but since
// it's a reference, nothing is freed
```

Example of Immutable Reference - Rust Programming

Structs are user-defined data types that allow you to group related values of different data types under one name. They are similar to structures in C/C++ or objects in other languages. They are primarily used to organize and represent data.

Struct - Rust Programming

Immutable references, which are also called shared references, enable you to retrieve a value without making any changes to it. Numerous immutable references can exist concurrently to a value.

University of Michigan - Ann Arbor

- Immutable Reference
- Mutable Reference

Types of References - Rust Programming

rust-lang.org

Mutable references, also known as exclusive references, allow you to access and modify a value. However, only one mutable reference to a value can exist within a given scope, ensuring that no data races occur.

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