Borrowed Data Escapes Outside of Closure

Understanding the Error Message

The error message "Borrowed data escapes outside of closure" indicates that a reference to borrowed data is being used outside of the scope where it was originally borrowed. This can occur when a closure captures a reference to borrowed data, and the closure is then used after the borrowed data is no longer valid.

Example Code

The following code demonstrates the error: ```rust let mut fields = Vec::new(); let mut a = 1; let mut b = 2; { let closure = || { // Attempt to mutate borrowed data a += 1; b += 1; // Use the borrowed data println!("a: {}, b: {}", a, b); }; // Closure escapes the scope } // Borrowed data is no longer valid ``` In this example, the closure captures references to the borrowed data `a` and `b`. However, the closure is then used after the borrowed data is no longer valid, causing the error.

Solution

To resolve the error, ensure that the borrowed data is still valid when the closure is used. This can be achieved by either borrowing the data for a shorter lifetime or by cloning the data before capturing it in the closure. In the above example, the error can be resolved by cloning the data before capturing it in the closure: ```rust let mut fields = Vec::new(); let a = 1; let b = 2; { let a = a.clone(); let b = b.clone(); let closure = || { // Mutate cloned data a += 1; b += 1; // Use the cloned data println!("a: {}, b: {}", a, b); }; // Closure escapes the scope } // Borrowed data is no longer valid ```