Rust

Ownership in one paragraph

Every value has one owner. Passing by value moves; borrow with & (shared, many) or &mut (exclusive, one). Shared and mutable references cannot coexist. Most "fights with the borrow checker" are a design smell — the data model mixed ownership and sharing.

Borrowing rules of thumb

• &T when you only read.
• &mut T when you mutate in place.
• T (by value) when you consume — builders, transforming constructors.
• Return owned types unless the caller clearly benefits from a borrow tied to a parameter's lifetime.

Lifetimes

• Start without annotations; add them when the compiler asks.
• 'static does not mean "lives forever" — it means "no non-static references inside". Prefer owned types over 'static juggling.
• If a struct needs many lifetimes, consider owned data or Arc instead.