# RuboCop, Types and Performance — Ruby

Source: https://www.geekswithgeeks.com/en/ruby/e-quality

> Keep Ruby code consistent and fast with RuboCop, optional typing and YJIT.

## Quality tools for a dynamic language

**RuboCop** is the standard linter and formatter, enforcing the community **Ruby Style Guide** and catching likely bugs; configure it in `.rubocop.yml`, autocorrect with `rubocop -a`, and add plugins such as `rubocop-rails` and `rubocop-rspec`. **Standard** is a zero-configuration alternative built on RuboCop. Because Ruby is dynamically typed, teams add **optional type checking** for large codebases: **RBS** is Ruby's official type signature language (in `.rbs` files), checked by **Steep**, and **Sorbet** (from Stripe) uses inline `sig` annotations with fast static and run-time checks. For **performance**, enable **YJIT** (`ruby --yjit` or `RUBY_YJIT_ENABLE=1`), which speeds up real Rails applications noticeably, and profile before optimising with **stackprof**, **rack-mini-profiler** and **memory_profiler**. Common wins in Ruby apps are not language-level: eliminating N+1 database queries, caching, background jobs and avoiding unnecessary object allocations in hot paths.

## A RuboCop config and a Sorbet signature

Consistent style plus gradual typing.

```ruby
# .rubocop.yml
# require:
#   - rubocop-rspec
# AllCops:
#   TargetRubyVersion: 3.4
#   NewCops: enable
# Style/StringLiterals:
#   EnforcedStyle: double_quotes
# Metrics/MethodLength:
#   Max: 15

# Sorbet: gradual static typing with inline signatures
# (the '# typed: true' sigil goes on the first line of the file)
require "sorbet-runtime"

class ShippingCalculator
  extend T::Sig

  sig { params(total_paise: Integer, express: T::Boolean).returns(Integer) }
  def fee_paise(total_paise, express:)
    return 0 if total_paise >= 100_000
    express ? 9_900 : 4_900
  end
end

# RBS alternative in sig/shipping_calculator.rbs:
# class ShippingCalculator
#   def fee_paise: (Integer total_paise, express: bool) -> Integer
# end

# run with YJIT:  RUBY_YJIT_ENABLE=1 bundle exec puma
```

## Fix the database before the language

Most slow Ruby web requests are slow because of database queries or external calls. Check query counts and response times first; YJIT and micro-optimisations come after.

**Quiz:** What is YJIT?

- [ ] A testing framework
- [ ] A package manager
- [x] A just-in-time compiler built into CRuby that speeds up Ruby code
- [ ] A linter

*Answer:* A just-in-time compiler built into CRuby that speeds up Ruby code. YJIT compiles hot Ruby code to machine code at run time.