CodeSandwich

fn nested_borrow_outlives_value() {
    let value = "abc".to_string();  // crate value
    let borrow = &value;            // create borrow
                                    // with lifetime of value
    let my_box = Box::new(borrow);  // create my_box
                                    // with lifetime of borrow,
                                    // which is lifetime of value
    return my_box                   // <COMPILE TIME FAIL>
                                    // my_box is not deleted,
                                    // but value is deleted,

CodeSandwich

fn value_moved_during_borrow_lifetime() {
    let value = "abc".to_string();  // crate value
    let borrow = &value;            // create borrow
    let my_box = Box::new(value);   // <COMPILE TIME FAIL> move of value
                                    // while borrowed
}

CodeSandwich

fn borrow_outlives_value() -> &String {
    let value = "abc".to_string();  // crate value
    let borrow = &value;            // create borrow
    return borrow                   // borrow is not deleted
                                    // <COMPILE TIME FAIL> delete value,
                                    // but it's still borrowed 
}

CodeSandwich

fn valid_flow() {
    let value = "abc".to_string();  // crate value
    let borrow = &value;            // create borrow
    println!("{}", value);          // use value without moving it
    println!("{}", borrow);         // use borrow
                                    // delete borrow
                                    // delete value safely, because
                                    // it's no longer borrowed 
}

CodeSandwich

struct MyStruct {                       // structure definition
    my_box: Box<u32>,                   // it has only 1 field,
                                        // a Box keeping integer on heap
}

fn my_fn() {
    let my_struct = MyStruct {          // create instance of structure
        my_box: Box::new(1234),         // acquire memory
    };
    println!("{}", my_struct.my_box);   // use

CodeSandwich

fn my_fn() {
    let my_box = Box::new(1234);    // acquire
    println!("{}", my_box);         // use
                                    // delete my_box,
                                    // which releases memory
}

CodeSandwich

main {
    A = allocate()  // A's lifetime begins
    do_stuff(A)     // use A
    B = A           // B's lifetime begins
    do_stuff(B)     // use B
    release(A)      // release, A's and B's lifetimes end
    do_stuff(A)     // <RUN TIME FAIL> use A after its lifetime ended
    do_stuff(B)     // <RUN TIME FAIL> use B after its lifetime ended
}

CodeSandwich

main {
    A = allocate()      // acquire
    do_stuff(A)         // use
    release(A)          // release, pointer owns allocation
                        // delete pointer
}

do_stuff(B) {
    do_more_stuff(B)    // use
                        // don't release, pointer doesn't own allocation

CodeSandwich

main {
   ...
   A = <pointer to>──────┐
   ...                   |
}                        │
                         ▼
╔══ HEAP ALLOCATED ════════╗
║ AA = "reachable"         ║
║ AB = <pointer to>──────┐ ║
╚════════════════════════│═╝

CodeSandwich

main {
    A = allocate()  // acquire
    do_stuff(A)     // use
    release(A)      // release
    release(A)      // <RUN TIME FAIL> release invalid pointer
                    // delete pointer
}