Ruby

Ruby is a dynamic, pure object-oriented language favored for Rails, scripting, and developer happiness.

Reserved Words

• __FILE__, __LINE__, BEGIN, END
• alias, and, begin, break
• case, class, def, defined?
• do, else, elsif, end, ensure
• false, for, if, in
• module, next, nil, not
• or, redo, rescue, retry
• return, self, super, then
• true, undef, unless, until
• when, while, yield

Core Object Model

• Everything is an object, even classes and integers.
• Open classes allow runtime extension (`class String; end`).
• Mixins with modules share behavior without inheritance.
• Symbols (e.g., :status) are immutable interned labels.
• Blocks, Procs, and Lambdas encapsulate behavior for iteration.

Syntax Highlights

• String interpolation: "Hello #{name}".
• Ranges: (1..10) inclusive, (1...10) exclusive.
• Keyword arguments with defaults: `def create(user:, admin: false)`.
• Safe navigation: `user&.profile&.city`.
• Pipelines via Enumerator::Lazy and pattern matching (Ruby 3+).

Essential Classes & Methods

• Enumerable: map, select, reject, reduce, any?, all?, chunk, group_by.
• Array: push/pop, shift/unshift, sample, zip, transpose, combination.
• Hash: fetch, dig, transform_keys, symbolize_keys (ActiveSupport).
• String: gsub, sub, split, strip, chars, each_line.
• Kernel: puts, print, p, loop, require, raise.
• File: open, read, write, each_line, binmode.

Operators

• Arithmetic: + - * / % **
• Comparison: == != < > <= >= <=>
• Logical: && || ! not and or
• Assignment: = += -= *= /= %= **= ||= &&=
• Range: .. ...
• Defined? and ternary: condition ? a : b

Frameworks & Tooling

• Ruby on Rails for full-stack web apps.
• Hanami, Sinatra, and Roda for lighter services.
• Bundler manages gems (`bundle init`, `bundle install`).
• Rake provides task automation, similar to makefiles.
• RSpec, Minitest, and Cucumber for testing.

Best Practices

• Favor symbols for keys, freeze constants, and leverage immutable data.
• Use RuboCop for linting and formatting.
• Encapsulate metaprogramming behind clear APIs.
• Prefer enumerators and lazy evaluation for large datasets.
• Adopt the "Convention over Configuration" mindset when using Rails.

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