18.1 Overview of Collections and Comparison with C

A useful way to appreciate Rust’s collection types is to compare them with C’s approach. In C, you often build dynamic arrays by manually calling malloc to allocate memory, realloc to resize, and free to release resources. Mistakes in these steps can lead to memory leaks, dangling pointers, or buffer overflows.

Rust addresses these issues by providing standard-library collection types that:

  1. Handle memory allocation and deallocation automatically,
  2. Enforce strict type safety,
  3. Use clear and well-defined ownership rules.

By relying on Rust’s collection types, you avoid common errors (e.g., forgetting to free allocated memory or writing out of bounds). Rust’s zero-cost abstractions mean performance is comparable to carefully optimized C code but without the usual risks.

The main collection types include:

  • Vec<T> for a growable, contiguous sequence (a “vector”),
  • String for growable, UTF-8 text,
  • HashMap<K, V> for key-value associations,
  • Plus various other structures (BTreeMap, HashSet, BTreeSet, VecDeque, etc.) for specialized needs.

Each collection automatically frees its memory when it goes out of scope, eliminating most manual resource-management tasks.