Immutable

NSArray, NSDictionary, and Collections

Working with Objective-C's core collection classes — NSArray, NSDictionary, NSSet — including mutability, enumeration, and common pitfalls.

String Library in Lua

Master Lua's built-in string library -- immutable strings, extraction, case conversion, lightweight pattern matching, and formatted output.

Immutable Data Structures

Explore Clojure's core persistent data structures — vectors, lists, maps, and sets — and understand how immutability and structural sharing make them both safe…

Mutable vs Immutable Collections

Understand Scala's two parallel collection hierarchies, why immutability is the default, and when it's worth reaching for a mutable collection instead.