```ruby
require 'ostruct'

class StrictOpenStruct < OpenStruct
  # Raises NoMethodError if the called method is not a setter and was not explicitly initialized with a value.
  def method_missing(method_name, *args, &block)
    if respond_to?(method_name) || method_name =~ /=$/
      super
    else
      fail NoMethodError, "undefined method `#{method_name}' for #{self}"
    end
  end
end
```

Refactor so we don't inherit from core class
user
```ruby
require 'ostruct'

class StrictOpenStruct

  def initialize(*args)
    @open_struct = OpenStruct.new(*args)
  end

  # Raises NoMethodError unless the underlying OpenStruct
  # responds to the method or the method is a setter
  def method_missing(method_name, *args, &block)
    if @open_struct.respond_to?(method_name) || method_name =~ /=$/
      @open_struct.send(method_name, *args, &block)
    else
      fail NoMethodError, "undefined method `#{method_name}' for #{self}"
    end
  end
end
```
assistant