Summary - Slices
- Rust course
- Beginner
- Lesson 59/115
- 5 min
Combine string and array slices to write a first-word function.
Slices summary
A slice is a borrowed view of contiguous data: &str for text, &[T] for arrays and vectors. Ranges take the forms a..b (b excluded), a..=b (included), ..b, a.. and ... String indexes are byte positions; slicing off a char boundary panics, and the safe option is get. Taking slices in function parameters is the most flexible choice.
What to choose when?
If you only read the data, take a slice; if you return a part of the input, return a slice. If you produced new data (joining, uppercasing), return an owned type: String or Vec<T>. Since a slice can't outlive its source, returning a slice of a local variable is a compile error.
Practice Last n elements
Write fn son_n(v: &[i32], n: usize) -> &[i32]; it returns &v[v.len() - n..]. Print the result for [1, 2, 3, 4, 5] and n = 2 with {:?}.
Starter code
fn main() {
// buraya yaz
}Sample solution
fn son_n(v: &[i32], n: usize) -> &[i32] {
&v[v.len() - n..]
}
fn main() {
let a = [1, 2, 3, 4, 5];
println!("{:?}", son_n(&a, 2));
}Expected output
[4, 5]
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 For <code>let v = [1, 2, 3, 4]; let s = &v[1..3];</code>, what is <code>s.len()</code>?
- 1
- 2 Correct answer
- 3
- 4
Explanation: The range 1..3 covers indexes 1 and 2: [2, 3].
2 Safe slice
let s = "abc";
let x = s.____(1..5); // Nonelet s = "abc";
let x = s.get(1..5); // NoneExplanation: get returns None instead of panicking on an out-of-bounds range.
3 Type and meaning
| Term | Meaning |
|---|---|
&str |
Text slice |
&[T] |
Element slice |
&mut [T] |
Mutable slice |
RangeInclusive |
a..=b |