Wait, You Can Do That in Ruby? — One Line Methods

As of Ruby 3.0, you can now define methods in one line (sometimes referred to as endless method definitions) such as the following:

  def invalid? = !valid?

Here is a more detailed example from a recent blog post of mine on writing ActiveRecord Style Macros:

  class Errors
    def initialize
      @h = Hash.new { |h, k| h[k] = [] }
    end

    def add(attribute, message) = (@h[attribute] << message)
    def [](attribute) = @h[attribute]
    def each(&block) = @h.each(&block)
    def empty? = @h.all? { |_, v| v.empty? }
    def any? = !empty?
    def clear = @h.clear
    def full_messages = @h.flat_map { |attribute, messages| messages.map { |message| "#{attribute} #{message}"} }
  end

Use responsibly. 😅