ruby
Ruby language conventions, idioms, and modern features (3.x+) for writing idiomatic Ruby code. Covers error handling patterns, performance optimization, and Ruby-specific idioms. Use when writing or reviewing pure Ruby code, using modern Ruby features (pattern matching, ractors, RBS), optimizing Ruby performance, or establishing Ruby conventions. For Rails-specific guidance use the rails skill. For design patterns use design-patterns-ruby. For testing use rspec. For code style use rubocop.
What this skill does
# Ruby Language Skill
## Error Handling Conventions
### Weirich raise/fail Convention
Use `fail` for first-time exceptions, `raise` only for re-raising:
```ruby
def process(order)
fail ArgumentError, "Order cannot be nil" if order.nil?
begin
gateway.charge(order)
rescue PaymentError => e
logger.error("Payment failed: #{e.message}")
raise # re-raise with raise
end
end
```
### Custom Exception Hierarchies
Group domain exceptions under a base error:
```ruby
module MyApp
class Error < StandardError; end
class PaymentError < Error; end
class InsufficientFundsError < PaymentError; end
end
# Rescue at any granularity:
rescue MyApp::InsufficientFundsError # specific
rescue MyApp::PaymentError # category
rescue MyApp::Error # all app errors
```
### Result Objects for Expected Failures
Use result objects instead of exceptions for expected failure paths:
```ruby
class Result
attr_reader :value, :error
def self.success(value) = new(value: value)
def self.failure(error) = new(error: error)
def initialize(value: nil, error: nil) = (@value, @error = value, error)
def success? = error.nil?
def failure? = !success?
end
```
### Caller-Supplied Fallback
Let callers define error handling via blocks:
```ruby
def fetch_user(id, &fallback)
User.find(id)
rescue ActiveRecord::RecordNotFound => e
fallback ? fallback.call(e) : raise
end
user = fetch_user(999) { |_| User.new(name: "Guest") }
```
See `references/error_handling.md` for full patterns and retry strategies.
## Modern Ruby (3.x+)
### Pattern Matching
```ruby
case response
in { status: 200, body: { users: [{ name: }, *] } }
"First user: #{name}"
in { status: (400..), error: message }
"Error: #{message}"
end
# Find pattern
case array
in [*, String => str, *]
"Found string: #{str}"
end
# Pin operator
expected = 200
case response
in { status: ^expected, body: }
process(body)
end
```
### Other 3.x+ Features
```ruby
# Endless methods (3.0+)
def square(x) = x * x
def admin? = role == "admin"
# Numbered block parameters (2.7+)
[1, 2, 3].map { _1 * 2 }
# Data class - immutable value objects (3.2+)
Point = Data.define(:x, :y)
p = Point.new(x: 1, y: 2)
p.with(x: 3) # => Point(x: 3, y: 2)
# Hash#except (3.0+)
params.except(:password, :admin)
# filter_map (2.7+) - select + map in one pass
users.filter_map { |u| u.email if u.active? }
# tally (2.7+)
%w[a b a c b a].tally # => {"a"=>3, "b"=>2, "c"=>1}
```
See `references/modern_ruby.md` for ractors, fiber scheduler, RBS types, and advanced pattern matching.
## Performance Quick Wins
### Frozen String Literals
```ruby
# frozen_string_literal: true
# Add to top of every file. Prevents mutation, reduces allocations.
# When you need mutable: String.new("hello") or +"hello"
```
### Efficient Enumeration
```ruby
# each_with_object for building results (avoids intermediate arrays)
totals = items.each_with_object(Hash.new(0)) do |item, hash|
hash[item.category] += item.amount
end
# Lazy enumerables for large/infinite sequences
(1..Float::INFINITY).lazy.select(&:odd?).map { _1 ** 2 }.first(10)
```
### Memoization with nil/false Caveat
```ruby
# Simple (only works if result is truthy)
def users = @users ||= User.all.to_a
# Safe (handles nil/false results)
def feature_enabled?
return @feature_enabled if defined?(@feature_enabled)
@feature_enabled = expensive_check
end
```
### String Building
```ruby
# Bad: O(n^2) with +=
result = ""; items.each { |i| result += i.to_s }
# Good: O(n) with <<
result = String.new; items.each { |i| result << i.to_s }
# Best: join
items.map(&:to_s).join
```
See `references/performance.md` for YJIT, GC tuning, benchmarking, and profiling tools.
## Ruby Idioms to Prefer
### Guard Clauses
```ruby
def process(value)
return unless value
return unless value.valid?
# main logic here
end
```
### Literal Array Constructors
```ruby
STATES = %w[draft published archived] # word array
FIELDS = %i[name email created_at] # symbol array
```
### Hash#fetch for Required Keys
```ruby
config.fetch(:api_key) # raises KeyError if missing
config.fetch(:timeout, 30) # default value
config.fetch(:handler) { build_handler } # lazy default
```
### Safe Navigation
```ruby
user&.profile&.avatar_url # returns nil if any link is nil
```
### Predicate and Bang Conventions
- `?` suffix: returns boolean (`empty?`, `valid?`, `admin?`)
- `!` suffix: dangerous version - mutates receiver or raises on failure (`save!`, `sort!`)
- Always provide a non-bang alternative when defining bang methods
## References
- `references/modern_ruby.md` - Pattern matching, ractors, fiber scheduler, RBS types
- `references/error_handling.md` - Exception hierarchies, result objects, retry patterns
- `references/performance.md` - YJIT, GC tuning, benchmarking, profiling
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