# Revision and Interview Questions — Ruby

Source: https://www.geekswithgeeks.com/en/ruby/p-revision

> Recall Ruby concepts quickly for exams and interviews.

## Cheat sheet

**Basics**: everything is an object; only `nil` and `false` are falsy; strings vs symbols; `# frozen_string_literal: true`; Integer, Float, BigDecimal for money; `Integer()` vs `to_i`. **Tools**: version managers, irb, gems, Bundler, Gemfile and Gemfile.lock, `bundle exec`, `~>` constraints. **Control**: expressions return values, `unless`, modifiers, `case/when` with `===` (ranges, classes, regexes), ranges including endless ones. **Collections**: Array, Hash (symbol keys, value omission), Enumerable (`map`, `select`, `reduce`, `group_by`, `tally`, `partition`, `each_with_object`, `filter_map`), bang methods, `&:sym`, lazy enumerators. **Blocks**: `yield`, `block_given?`, `&block`, `_1` and `it`, procs vs lambdas, closures. **OOP**: `initialize`, `attr_reader`, class methods with `self.`, `?`/`!` conventions, endless methods, modules as namespaces and mixins, `include`/`extend`/`prepend`, Enumerable and Comparable, `ancestors`, single inheritance with `super`, public/private/protected, Struct and Data. **Methods**: positional, defaults, splats, keyword and required keyword arguments, `**opts`, `(...)` forwarding. **Errors**: `raise`, `rescue`, `else`, `ensure`, `retry`, custom errors under StandardError. **Pattern matching**: `case/in`, `=>`, `in`, guards, pin, `deconstruct_keys`. **Meta**: duck typing, open classes, refinements, `send`, `define_method`, `method_missing` with `respond_to_missing?`, DSLs with `instance_eval`. **Practical**: File, JSON, CSV, Time, regex anchors `\A`/`\z`, GVL, threads for I/O, Ractors, fibers. **Ecosystem**: gems and SemVer, RSpec and Minitest, RuboCop, RBS/Sorbet, YJIT, Rails MVC.

## Common interview questions

Answer each with a short code example.

```text
1. What does it mean that everything in Ruby is an object?
2. Which values are falsy in Ruby?
3. What is the difference between a symbol and a string?
4. Explain blocks, procs and lambdas and how they differ.
5. include vs extend vs prepend?
6. How does method lookup work (ancestors)?
7. What are bang (!) and predicate (?) methods?
8. How does case/when use ===? How does case/in differ?
9. What is the GVL, and when do threads help?
10. What are method_missing and respond_to_missing? for?
11. What problems can monkey patching cause, and what are refinements?
12. Explain Gemfile vs Gemfile.lock and what bundle exec does.
```

## Show idiomatic code

Interviewers for Ruby roles look for idiomatic style. Rewriting a loop as a short Enumerable chain, and explaining why it is clearer, is a quick way to demonstrate fluency.

**Quiz:** Which method do you define to make your own class work with Enumerable?

- [ ] to_s
- [ ] initialize
- [ ] inspect
- [x] each

*Answer:* each. Enumerable builds its methods on each.