Return value
- Rust course
- Beginner
- Lesson 32/115
- 4 min
Specify the return type with the -> arrow.
Return values
The return type is written with ->. The body's last expression (without a semicolon) is the return value; there's no need to write return:
fn kare(n: i32) -> i32 {
n * n // no semicolon → value returned
}
fn mutlak(n: i32) -> i32 {
if n < 0 { -n } else { n }
}Accidentally putting ; on the last line turns it into a statement and the function returns (); the compiler reports "mismatched types".
if is an expression
In Rust, if, match and blocks produce values; that's why no ternary operator (?:) is needed:
let yas = 20;
let durum = if yas >= 18 { "yetişkin" } else { "çocuk" };
let kdvli = {
let fiyat = 100.0;
fiyat * 1.2
};
println!("{durum} {kdvli}");The if-else arms must have the same type.
Practice Absolute value
Write the fn mutlak(n: i32) -> i32 function with an if expression and without writing return. Print mutlak(-7) and mutlak(4) on one line.
Starter code
fn main() {
// buraya yaz
}Sample solution
fn mutlak(n: i32) -> i32 {
if n < 0 { -n } else { n }
}
fn main() {
println!("{} {}", mutlak(-7), mutlak(4));
}Expected output
7 4
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Why doesn't <code>fn f() -> i32 { 5; }</code> compile?
- 5 isn't an i32
- return is missing and required
- It compiles
- 5; is a statement; the function returns () but i32 is expected Correct answer
Explanation: The semicolon turns the expression into a statement and discards its value; writing just 5 (or return 5;) compiles.
2 Return type
fn ortalama(a: f64, b: f64) ____ f64 {
(a + b) / 2.0
}fn ortalama(a: f64, b: f64) -> f64 {
(a + b) / 2.0
}Explanation: -> declares the function's return type.
3 Body and return
| Term | Meaning |
|---|---|
{ n * n } |
Returns n * n |
{ n * n; } |
Returns () |
if a { 1 } else { 2 } |
Expression |
return x; |
Explicit return |