modules

Ruby modules enable code sharing across classes without inheritance. I use include for instance methods, extend for class methods. prepend inserts module before class in method lookup. Concerns organize shared behavior—validations, scopes, association

Rust's module system uses mod to define modules and pub to control visibility. Modules can be inline (mod name { ... }) or in separate files (mod name; loads name.rs). By default, items are private; use pub to expose them. I organize code into modules