ruby-idioms

Ruby Idioms

Iron Laws

1. Prefer simple objects over metaprogramming
2. Raise exceptions for failures; return values for expected branches
3. Keep mutation narrow and obvious
4. Wrap third-party APIs behind project-owned adapters
5. Avoid global state and hidden thread-local coupling
6. Consider it for simple single-argument blocks when clarity permits
7. Prefer pattern matching for complex data destructuring
8. Enable YJIT in production (Ruby 3.2+; Rails 7.2+ enables by default on Ruby 3.3+)

Ruby 3.4+ Features

The it Keyword

# Before
users.map { |user| user.name }
orders.select { |o| o.completed? }

# After (Ruby 3.4+)
users.map { it.name }
orders.select { it.completed? }

Use when: Single argument, 1-2 method calls, no nesting
Avoid when: Multiple args, complex logic, nested blocks

Pattern Matching

case response
in { status: 200, body: { data: items } }
  items
in { status: 404 }
  raise NotFoundError
in { status: code, body: { error: msg } }
  raise ApiError.new("#{code}: #{msg}")
end

Use for: Complex data structures, state machines, event handling
Avoid for: Simple cases (use if/when instead)

YJIT (Ruby 3.2+) — Current Recommendation

YJIT is the production-ready JIT compiler for Ruby 3.x:

# Check if YJIT is enabled
RubyVM::YJIT.enabled?  # => true

# Enable in production:
# Environment variable: RUBY_YJIT_ENABLE=1
# Or in code before app loads: RubyVM::YJIT.enable

Benefits: 15-30% performance improvement for Rails apps

Status:

• Bare Ruby: Not enabled by default; enable via RUBY_YJIT_ENABLE=1 or RubyVM::YJIT.enable
• Rails 7.2+: Enabled by default when running on Ruby 3.3+

ZJIT (Ruby 4.0+) — Experimental

ZJIT is the next-generation JIT compiler in Ruby 4.0:

# Verify ZJIT is enabled (Ruby 4.0+)
puts RubyVM::ZJIT.enabled?  # => true

# Enable: ruby --zjit (CLI) or RubyVM::ZJIT.enable (runtime)

Status: Experimental/not recommended for production; YJIT remains the recommended JIT for Ruby 3.2-4.0