3.3 Statements and Expressions
About 2 min
3.3 Statements and Expressions κ΄λ ¨
Rust By Practice
Rust By Practice
Examples
fn main() {
let x = 5u32;
let y = {
let x_squared = x * x;
let x_cube = x_squared * x;
// This expression will be assigned to `y`
x_cube + x_squared + x
};
let z = {
// The semicolon suppresses this expression and `()` is assigned to `z`
2 * x;
};
println!("x is {:?}", x);
println!("y is {:?}", y);
println!("z is {:?}", z);
}
//
//
/*
x is 5
y is 155
z is ()
*/
Exercises
1. ππ
πProblem
// Make it work with two ways
fn main() {
let v = {
let mut x = 1;
x += 2
};
assert_eq!(v, 3);
println!("Success!");
}
//
//
/*
Compiling playground v0.0.1 (/playground)
error[E0308]: mismatched types
--> src/main.rs:8:4
|
8 | assert_eq!(v, 3);
| ^^^^^^^^^^^^^^^^
| |
| expected `()`, found integer
| expected because this is `()`
|
= note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
For more information about this error, try `rustc --explain E0308`.
error: could not compile `playground` (bin "playground") due to previous error
*/
Solution 1
// Make it work with two ways
fn main() {
let v = {
let mut x = 1;
x += 2
};
assert_eq!(v, ());
println!("Success!");
}
//
//
/*
Success!
*/
Solution 2
// Make it work with two ways
fn main() {
let v = {
let mut x = 1;
x += 2;
x
};
assert_eq!(v, 3);
println!("Success!");
}
//
//
/*
Success!
*/
2. π
πProblem
fn main() {
let v = (let x = 3);
assert!(v == 3);
println!("Success!");
}
//
//
/*
Compiling playground v0.0.1 (/playground)
error: expected expression, found `let` statement
--> src/main.rs:3:13
|
3 | let v = (let x = 3);
| ^^^
error: expected expression, found statement (`let`)
--> src/main.rs:3:13
|
3 | let v = (let x = 3);
| ^^^^^^^^^
|
= note: variable declaration using `let` is a statement
error[E0658]: `let` expressions in this position are unstable
--> src/main.rs:3:13
|
3 | let v = (let x = 3);
| ^^^^^^^^^
|
= note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
warning: unnecessary parentheses around assigned value
--> src/main.rs:3:12
|
3 | let v = (let x = 3);
| ^ ^
|
= note: `#[warn(unused_parens)]` on by default
help: remove these parentheses
|
3 - let v = (let x = 3);
3 + let v = let x = 3;
|
error[E0308]: mismatched types
--> src/main.rs:5:17
|
5 | assert!(v == 3);
| - ^ expected `bool`, found integer
| |
| expected because this is `bool`
Some errors have detailed explanations: E0308, E0658.
For more information about an error, try `rustc --explain E0308`.
warning: `playground` (bin "playground") generated 1 warning
error: could not compile `playground` (bin "playground") due to 4 previous errors; 1 warning
*/
Solution
fn main() {
let v = {
let x = 3;
x
};
assert!(v == 3);
println!("Success!");
}
//
//
/*
Success!
*/
3. π
πProblem
fn main() {
let s = sum(1 , 2);
assert_eq!(s, 3);
println!("Success!");
}
fn sum(x: i32, y: i32) -> i32 {
x + y;
}
//
//
/*
Compiling playground v0.0.1 (/playground)
error[E0308]: mismatched types
--> src/main.rs:9:27
|
9 | fn sum(x: i32, y: i32) -> i32 {
| --- ^^^ expected `i32`, found `()`
| |
| implicitly returns `()` as its body has no tail or `return` expression
10 | x + y;
| - help: remove this semicolon to return this value
For more information about this error, try `rustc --explain E0308`.
error: could not compile `playground` (bin "playground") due to previous error
*/
Solution
fn main() {
let s = sum(1 , 2);
assert_eq!(s, 3);
println!("Success!");
}
fn sum(x: i32, y: i32) -> i32 {
return x + y;
}
//
//
/*
Success!
*/
