Blocks and Scopes
- A block in Rust contains a sequence of expressions, enclosed by braces
{}
. - The final expression of a block determines the value and type of the whole block.
fn main() { let z = 13; let x = { let y = 10; dbg!(y); z - y }; dbg!(x); // dbg!(y); }
If the last expression ends with ;
, then the resulting value and type is ()
.
A variable’s scope is limited to the enclosing block.
This slide should take about 5 minutes.
-
You can explain that dbg! is a Rust macro that prints and returns the value of a given expression for quick and dirty debugging.
-
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
. -
Demonstrate that attempting to access
y
outside of its scope won’t compile. -
Values are effectively “deallocated” when they go out of their scope, even if their data on the stack is still there.