internal_dsl_with_instance_eval

📜 Building Internal DSLs with instance_eval

Use instance_eval to execute a block in the context of an object, switching self so DSL methods read like native language constructs. This approach leverages closures to capture environment and define concise APIs for configuration or markup.

class HTMLBuilder
  def initialize(&block)
    @result = ''
    instance_eval(&block)
  end

  def element(name, content = nil, &block)
    @result << "<#{name}>"
    if block
      instance_eval(&block)
    else
      @result << content.to_s
    end
    @result << "</#{name}>"
  end

  def to_s
    @result
  end
end

html = HTMLBuilder.new do
  element :p, 'Hello'
  element :div do
    element :span, 'Nested'
  end
end

puts html.to_s