Overview

Endless method definition provides a streamlined syntax for writing short, single-expression methods in Ruby. Instead of using the traditional def...end block structure, you can define methods using the = operator followed by the method body on the same line.

This feature addresses the common pattern of methods that simply return the result of a single expression, making the code more compact and readable for simple operations.

# Traditional syntax
def square(x)
  x * x
end

# Endless method syntax
def square(x) = x * x

The endless method syntax is particularly useful for:

• Mathematical operations and calculations
• Simple data transformations
• Accessor methods with slight modifications
• Methods that return single values or expressions

Ruby treats endless methods identically to traditional methods in terms of visibility, inheritance, and method dispatch. They support all standard method features including parameters, keyword arguments, and block parameters.

class Calculator
  def add(a, b) = a + b
  def multiply(a, b) = a * b
  def percentage(value, total) = (value.to_f / total * 100).round(2)
end

calc = Calculator.new
calc.add(5, 3)        # => 8
calc.percentage(25, 80) # => 31.25

Basic Usage

Endless method definition uses the def method_name(parameters) = expression syntax. The expression after the equals sign becomes the return value of the method.

class Person
  def initialize(first, last)
    @first_name = first
    @last_name = last
  end

  def full_name = "#{@first_name} #{@last_name}"
  def initials = "#{@first_name[0]}#{@last_name[0]}"
  def name_length = full_name.length
end

person = Person.new("John", "Doe")
person.full_name    # => "John Doe"
person.initials     # => "JD"
person.name_length  # => 8

Endless methods support all parameter types including optional parameters, keyword arguments, and splat operators:

class StringProcessor
  def truncate(text, length = 50) = text.length > length ? text[0...length] + "..." : text
  def format_name(first:, last:) = "#{last}, #{first}"
  def join_words(*words, separator: " ") = words.join(separator)
end

processor = StringProcessor.new
processor.truncate("This is a long sentence that needs truncation", 20)
# => "This is a long sente..."

processor.format_name(first: "Jane", last: "Smith")
# => "Smith, Jane"

processor.join_words("Ruby", "is", "awesome", separator: "-")
# => "Ruby-is-awesome"

You can use endless methods for simple conditional logic and method chaining:

class User
  attr_reader :age, :premium

  def initialize(age, premium = false)
    @age = age
    @premium = premium
  end

  def adult? = age >= 18
  def senior? = age >= 65
  def discount_rate = premium ? 0.15 : (senior? ? 0.10 : 0.05)
  def display_status = "#{adult? ? 'Adult' : 'Minor'} #{premium ? '(Premium)' : ''}"
end

user = User.new(25, true)
user.adult?         # => true
user.discount_rate  # => 0.15
user.display_status # => "Adult (Premium)"

Endless methods work with class methods and module methods:

module MathUtils
  def self.factorial(n) = n <= 1 ? 1 : n * factorial(n - 1)
  def self.fibonacci(n) = n <= 1 ? n : fibonacci(n - 1) + fibonacci(n - 2)
end

class Temperature
  def self.celsius_to_fahrenheit(celsius) = celsius * 9.0 / 5 + 32
  def self.fahrenheit_to_celsius(fahrenheit) = (fahrenheit - 32) * 5.0 / 9
end

MathUtils.factorial(5)  # => 120
Temperature.celsius_to_fahrenheit(25)  # => 77.0

Advanced Usage

Endless methods can handle complex expressions and method chains, making them suitable for more sophisticated operations while maintaining readability:

class DataProcessor
  def process_scores(scores) = scores.map(&:to_f).select { |s| s >= 0 }.sort.reverse
  def average(numbers) = numbers.empty? ? 0 : numbers.sum.to_f / numbers.size
  def normalize_text(text) = text.strip.downcase.gsub(/\s+/, ' ')
end

processor = DataProcessor.new
processor.process_scores(['85', '92', '78', '-5', '88'])
# => [92.0, 88.0, 85.0, 78.0]

processor.average([85, 92, 78, 88])  # => 85.75
processor.normalize_text("  Hello    World  ")  # => "hello world"

Endless methods integrate with Ruby's functional programming features, including blocks and higher-order functions:

class ListProcessor
  def map_with_index(array, &block) = array.each_with_index.map(&block)
  def filter_map(array, &block) = array.filter_map(&block)
  def partition_by_type(array, type) = array.partition { |item| item.is_a?(type) }
  def group_by_length(strings) = strings.group_by(&:length)
end

processor = ListProcessor.new
words = ['cat', 'elephant', 'dog', 'butterfly']

processor.map_with_index(words) { |word, i| "#{i}: #{word}" }
# => ["0: cat", "1: elephant", "2: dog", "3: butterfly"]

processor.group_by_length(words)
# => {3=>["cat", "dog"], 8=>["elephant"], 9=>["butterfly"]}

You can use endless methods for creating fluent interfaces and method chaining patterns:

class QueryBuilder
  def initialize(table) = @query = "SELECT * FROM #{table}"
  def where(condition) = tap { @query += " WHERE #{condition}" }
  def order_by(column) = tap { @query += " ORDER BY #{column}" }
  def limit(count) = tap { @query += " LIMIT #{count}" }
  def to_sql = @query
end

query = QueryBuilder.new('users')
  .where('age > 18')
  .order_by('name')
  .limit(10)
  .to_sql
# => "SELECT * FROM users WHERE age > 18 ORDER BY name LIMIT 10"

Endless methods work effectively with pattern matching and case expressions:

class ResponseHandler
  def status_message(code) = case code
    when 200..299 then "Success"
    when 300..399 then "Redirect"
    when 400..499 then "Client Error"
    when 500..599 then "Server Error"
    else "Unknown Status"
  end

  def parse_response(response) = response => { status:, body: }; process_body(body, status)
  def process_body(body, status) = status < 400 ? JSON.parse(body) : { error: body }
end

handler = ResponseHandler.new
handler.status_message(404)  # => "Client Error"

Common Pitfalls

The most frequent mistake with endless methods is attempting to use multiple statements or complex control flow. Endless methods can only contain a single expression:

# WRONG: Multiple statements
def process_data(data) = data.clean; data.validate; data.save

# WRONG: Complex control flow
def calculate_tax(income) =
  if income < 20000
    0
  elsif income < 50000
    income * 0.1
  else
    income * 0.2
  end

# CORRECT: Single expression with ternary operator
def calculate_tax(income) = income < 20000 ? 0 : (income < 50000 ? income * 0.1 : income * 0.2)

# BETTER: Use traditional method for complex logic
def calculate_tax(income)
  return 0 if income < 20000
  return income * 0.1 if income < 50000
  income * 0.2
end

Another common issue is misunderstanding operator precedence with endless methods:

# Potentially confusing precedence
def calculate(a, b) = a + b * 2  # This is a + (b * 2), not (a + b) * 2

# Clear with parentheses
def calculate_sum_doubled(a, b) = (a + b) * 2
def calculate_with_multiplier(a, b) = a + (b * 2)

# Testing precedence
def test_method(x) = x > 5 ? "big" : "small"  # Works as expected
def confusing_method(x) = x > 5 && x < 10 ? "medium" : x > 10 ? "big" : "small"  # Hard to read

Endless methods can create subtle issues with method visibility and scope:

class Example
  private

  def private_helper(x) = x * 2

  public

  def public_method(x) = private_helper(x) + 1  # This works fine

  # But this might be confusing about visibility
  def another_public(x) = self.private_helper(x) + 1  # NoMethodError!
end

example = Example.new
example.public_method(5)  # => 11
example.another_public(5)  # => NoMethodError: private method `private_helper'

Be careful with endless methods that modify state or have side effects, as they can hide important operations:

class Counter
  def initialize = @count = 0

  # This hides the side effect of incrementing
  def increment = @count += 1  # Returns new value, but mutation isn't obvious

  # More explicit about side effects
  def increment_and_return
    @count += 1
  end

  # Better for pure operations
  def next_value = @count + 1  # No side effects
end

Endless methods with complex return types can be harder to understand:

# Hard to understand what this returns
def complex_operation(data) = data.group_by(&:type).transform_values { |v| v.map(&:process).compact }

# More readable with intermediate variables in traditional method
def complex_operation(data)
  grouped = data.group_by(&:type)
  grouped.transform_values { |items| items.map(&:process).compact }
end

Reference

Syntax Forms

Supported Parameter Types

Method Types

Valid Expressions

Ruby Version Compatibility

Limitations