Borrowed Data Escapes Outside of Closure

Understanding the Error

The error "borrowed data escapes outside of closure" occurs when a reference to borrowed data is stored outside of the closure that created it. This can happen when a reference to a local variable is stored in a closure that outlives the variable, or when a reference to a mutable variable is stored in a closure that does not have a mutable borrow to the variable.

Example

Consider the following code: ``` fn main() { let a = 10; let b = &mut 20; let f = || { println!("a: {}, b: {}", a, *b); }; f(); } ``` This code will produce the error "borrowed data escapes outside of closure" because the reference to `a` and `b` is stored in the closure `f`, which outlives the scope of `a` and `b`.

Resolving the Error

There are a few ways to resolve this error: * **Move the borrowed data into the closure:** This can be done by using a `move` closure, which will move the borrowed data into the closure. * **Use a reference counted smart pointer:** This will allow the closure to borrow the data without requiring a mutable borrow. * **Clone the borrowed data:** This will create a copy of the borrowed data that the closure can borrow. In the example above, the error can be resolved by using a move closure: ``` fn main() { let a = 10; let b = &mut 20; let f = move || { println!("a: {}, b: {}", a, *b); }; f(); } ```