Blocks

A block in Rust has a value and a type: the value is the last expression of the block:

1. fn main() {
2. let x = {
3. let y = 10;
4. println!("y: {y}");
5. let z = {
6. let w = {
7. 3 + 4
8. };
9. println!("w: {w}");
10. y * w
11. };
12. println!("z: {z}");
13. z - y
14. };
15. println!("x: {x}");
16. }

The same rule is used for functions: the value of the function body is the return value:

1. fn double(x: i32) -> i32 {
2. x + x
3. }

5. fn main() {
6. println!("doubled: {}", double(7));
7. }

However if the last expression ends with ;, then the resulting value and type is ().

Key Points:

• The point of this slide is to show that blocks have a type and value in Rust.
• You can show how the value of the block changes by changing the last line in the block. For instance, adding/removing a semicolon or using a return.