Rust Systems Programming - Ownership, Borrowing & Concurrency

1. Each value in Rust has an owner variable.
2. There can only be one owner at a time.
3. When the owner goes out of scope, the value is automatically dropped.

Assigning a non-Copy variable to another transfers ownership (a move). The source variable becomes uninitialized and invalid, preventing double-free bugs at compile time without needing a garbage collector.

Borrowing grants temporary access to data without taking ownership.

Rules:
1. At any given time, you can have any number of immutable references (&T) OR exactly one mutable reference (&mut T).
2. References must always be valid (dangling references are caught at compile time).

Allowing multiple active references where at least one can mutate data leads to data races, iterator invalidation, and memory corruption. Rust prevents this at compile time by ensuring mutability is strictly exclusive.

NLL is a borrow checker capability where a reference's lifetime ends at its last point of use, rather than stretching to the end of its enclosing scope block. This removes many false-positive borrow errors.

Lifetime annotations describe the relationships between references' lifetimes across parameters and return values. They do not alter actual run-time lifespans; they assist the compiler in verifying that returned references remain valid.

1. Each elided reference parameter gets a distinct input lifetime annotation.
2. If there is exactly one input lifetime, it is assigned to all output lifetimes.
3. If an input parameter is &self or &mut self, its lifetime is assigned to all output lifetimes.