ruby

Ruby Language Skill

Error Handling Conventions

Weirich raise/fail Convention

Use fail for first-time exceptions, raise only for re-raising:

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:

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:

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:

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

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

# 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}