Borrowing and lifetime

We have used references in our code. A reference is an instance in the stack that points to another instance. Let's recall what an instance memory usage looks like:

Stack: ☐☒☐☐☐☐☐☐☐☐☐☐

         ↓

Heap:  ☐☒☒☒☒☐☐☐☐☐☐☐

A reference is allocated in stack memory, pointing to another instance:

Stack: ☐☒←☒☐☐☐☐☐☐☐☐

         ↓

Heap:  ☐☒☒☒☒☐☐☐☐☐☐☐

Allocating in the stack is cheaper than allocating in the heap. Because of this, using references most of the time is more efficient than cloning...