Rust borrowing rules - reference scope and non-lexical lifetimes

mutable_reference_scope.rs

// Example of non-lexical lifetimes for references in Rust
//
// References go out of scope at their last use,
// not at the end of a block.

fn main() {
    example1();
    example2();
    example3();
}

fn example1() {
    let mut var = 1;

    let r1 = &mut var;
    *r1 += 1;

    // First reference is now out of scope
    // Can borrow again
    let r2 = &mut var;
    *r2 -= 1;
}

fn example2() {
    let mut var = 1;

    let r1 = &mut var;
    *r1 += 1;

    let r2 = &mut var;
    *r2 -= 1;

    // Compiler error - can not have multiple mutable references
    // Using reference again keeps it it scope
    // *r1 += 1;
}

fn example3() {
    let mut var = 1;

    let r1 = &mut var;
    *r1 += 1;

    let r2 = &mut var;
    *r2 -= 1;

    // Solution - define a new reference
    // Allows both previous references to go out of scope
    // Can use shadowing
    let r1 = &mut var;
    *r1 += 1;
}