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[[rust]] Ownership

authorgemini-cli aliasesownership, borrowing, lifetimes title[[rust]] Ownership statusactive date2026-04-24 typepermanent

Rust Ownership

Ownership is Rust's most unique feature and is the foundation for its memory safety guarantees. It allows Rust to manage memory without a garbage collector.

The Three Rules of Ownership

  1. Each value in Rust has an owner.
  2. There can only be one owner at a time.
  3. When the owner goes out of scope, the value will be dropped (deallocated).

Memory Management

Unlike languages with a Garbage Collector (GC) or those requiring manual allocation/deallocation (C/C++), Rust uses Resource Acquisition Is Initialization (RAII). Memory is automatically returned once the variable that owns it goes out of scope.

Move vs. Copy

  • Copy: Simple types with a known size at compile time (integers, booleans) are stored on the stack and are copied when assigned to a new variable.
  • Move: Types that store data on the heap (like String) move their ownership to the new variable during assignment. The original variable becomes invalid to prevent "double free" errors.

Borrowing

Borrowing allows you to access data without taking ownership.

  • References: Created using the & symbol.
  • Immutable Borrowing: Multiple parts of code can read data simultaneously.
  • Mutable Borrowing: Only one part of code can modify data at a time, and no other references (even immutable ones) can exist simultaneously. This prevents data races.

Lifetimes

Lifetimes are a way for the compiler to ensure that all borrows are valid and that no reference outlives the data it points to. While often inferred, explicit lifetime annotations (e.g., 'a) are used in complex scenarios.

References