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Advanced 16 min readModule: Module 5: Slices & Memory Layout

Slices (&str, &[T]) & Memory Safety

Reference contiguous sub-sequences of collections with zero memory allocation using string and array slices.

What You Will Learn in This Lesson

  • What a slice is: a pointer to starting element + length
  • String slices (&str) vs heap-allocated String
  • Array slices (&[i32]) for generic contiguous sub-views

Introduction & Core Concept

A slice is a reference to a contiguous sequence of elements in a collection rather than the whole collection.
WHY DOES THIS MATTER IN THE REAL WORLD?

String slices (&str) allow functions to accept both String and literal strings without performing heap allocations.

First Word Extractor with String Slice

rust
rust
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fn first_word(s: &str) -> &str {
    let bytes = s.as_bytes();
    for (i, &item) in bytes.iter().enumerate() {
        if item == b' ' {
            return &s[0..i];
        }
    }
    &s[..]
}
 
fn main() {
    let greeting = "Hello World";
    println!("First word: {}", first_word(greeting));
}

Line-by-Line Technical Breakdown

1Slices prevent index-out-of-sync bugs because the borrow checker links the slice lifetime to the underlying data.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[RUST]
RUST SOURCE EDITOR
Interactive Live Code

Industry Best Practices & Professional Standards

  • Always use &str for function input arguments instead of &String.

Lesson Summary & Core Takeaways

  • Slices provide zero-cost views into contiguous memory segments.