Summary - Functions
- Rust course
- Beginner
- Lesson 35/115
- 5 min
Combine parameters, returns and expressions to build calculation functions.
Functions summary
fn name(param: Type) -> Return: parameter types are required, the return value is the last expression (without a semicolon), and return is used for early exits. if, match and blocks are value-producing expressions. Several values are returned with a tuple. Names are written in snake_case.
fn istatistik(s: &[i32]) -> (i32, f64) {
let toplam: i32 = s.iter().sum();
(toplam, toplam as f64 / s.len() as f64)
}Functions as values
Functions can be assigned to a variable like a value or passed to another function; their type looks like fn(i32) -> i32:
fn ikiye(n: i32) -> i32 { n * 2 }
fn uygula(f: fn(i32) -> i32, x: i32) -> i32 { f(x) }
println!("{}", uygula(ikiye, 21)); // 42Closures (anonymous functions) will make this idea even more powerful later.
Practice Statistics
Write the istatistik(s: &[i32]) -> (i32, f64) function above. Destructure with let (t, o) = istatistik(&[2, 4, 9]); and print println!("{t} {o}");.
Starter code
fn main() {
// buraya yaz
}Sample solution
fn istatistik(s: &[i32]) -> (i32, f64) {
let toplam: i32 = s.iter().sum();
(toplam, toplam as f64 / s.len() as f64)
}
fn main() {
let (t, o) = istatistik(&[2, 4, 9]);
println!("{t} {o}");
}Expected output
15 5
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does <code>istatistik(&[2, 4, 9])</code> return?
- (15, 5.0) Correct answer
- (15, 5)
- (5.0, 15)
- 15
Explanation: The sum is 15 (i32) and the average 15 / 3 = 5.0 (f64); the tuple order matches the signature.
2 Function type
fn uygula(f: ____, x: i32) -> i32 {
f(x)
}fn uygula(f: fn(i32) -> i32, x: i32) -> i32 {
f(x)
}Explanation: fn(i32) -> i32 is the type of a function taking an i32 and returning an i32.
3 Group summary
| Term | Meaning |
|---|---|
fn |
Definition |
-> T |
Return type |
Last expression |
Return value |
return |
Early exit |