Day 7: Slices

Slices are references to a contiguous sequence of elements - they don't own the data.

String Slices: &str

let s = String::from("hello world");
let hello = &s[0..5];   // "hello"
let world = &s[6..11];  // "world"

// Shorthand:
let hello = &s[..5];    // from start
let world = &s[6..];    // to end
let full = &s[..];      // entire string

Array Slices: &[T]

let arr = [1, 2, 3, 4, 5];
let slice: &[i32] = &arr[1..4];  // [2, 3, 4]

Why Slices Matter for Solana

Account data in Solana is accessed as byte slices (&[u8]). Understanding slices is essential!

The Task

Implement first_word that returns the first word in a string (up to the first space).

Requirements

• Return a &str slice of the input
• If no space found, return the entire string
• "hello world" → "hello"

Hints

// Iterate with index
for (i, c) in s.chars().enumerate() {
    if c == ' ' {
        return &s[..i];
    }
}

• Use .chars() to iterate over characters
• Use .enumerate() to get indices
• Use &s[..index] to slice from start
• Use &s[..] or just s to return the whole string