Here is another solution – creating a class AbbreviatedCampuses that all campuses register themselves with using AbbreviatedCampuses.register self. All campuses also implement an abbreviation method as the single place their abbreviation is written.

With this method, when you add a new campus, you only need to change one place in the code. But you don’t have to do the slow and hard-to-understand metaprogramming with ObjectSpace or Object.const_get – you explicitly link the new campus to the new registry. And the registration line in each campus class is shorter than the three-line self.campus_like? definition with the ObjectSpace solution.

class UnknownCampus
  def name
    "Unknown Campus"
  end

  def mascot
    "Unknown Mascot"
  end
end

class AbbreviatedCampuses
  @@campus_like_classes = Hash.new(UnknownCampus)

  def self.register(klass)
    abbreviation = klass.new.abbreviation
    @@campus_like_classes[abbreviation] = klass
  end

  def self.build_from(abbreviation)
    @@campus_like_classes[abbreviation].new
  end
end

# The above two classes must be loaded first.
# The rest can load in any order.

class CampusDetails
  def campus_name(abbreviation)
    AbbreviatedCampuses.build_from(abbreviation).name
  end

  def campus_mascot(abbreviation)
    AbbreviatedCampuses.build_from(abbreviation).mascot
  end
end

class UMNTC
  def name
    "University of Minnesota Twin Cities"
  end
  def mascot
    "Gopher"
  end
  def abbreviation
    "UMNTC"
  end

  AbbreviatedCampuses.register self
end

# snipped some repetitive campuses from this comment…

class UMNTCRO
  def name
    "University of Minnesota Rochester"
  end
  def mascot
    "Raptor"
  end
  def abbreviation
    "UMNTCRO"
  end

  AbbreviatedCampuses.register self
end

class CollegeInTheSchools
  def name
    "College in the Schools"
  end
  def mascot
    ""
  end
  def abbreviation
    "CITS"
  end

  AbbreviatedCampuses.register self
end

Some sample test code:

puts CampusDetails.new.campus_name("CITS")
puts CampusDetails.new.campus_mascot("UMNTCRO")
puts CampusDetails.new.campus_mascot("NOSUCH")

I think the two CampusDetails methods would be better off as class methods, defined like def self.campus_name, since they don’t have any instance variables. But I kept them instance methods in this solution for easy comparison.

Another solution: if all you need from the campuses is to get their data, you could just use a Hash instead.

Though this solution doesn’t support custom class behavior, it’s a lot simpler and more concise. This solution could apply before the step in the article when the CollegeInTheSchools class is added, which is presumed to have additional behavior.

class CampusDetails
  CAMPUS_LIKES_BY_ABBR = {
    "UMNTC" => {
      name: "University of Minnesota Twin Cities",
      mascot: "Gopher",
    },
    "UMNMO" => {
      name: "University of Minnesota Morris",
      mascot: "Cougar",
    },
    "UMNCR" => {
      name: "University of Minnesota Crookston",
      mascot: "Golden Eagle",
    },
    "UMNTCRO" => {
      name: "University of Minnesota Rochester",
      mascot: "Raptor",
    },
    "CITS" => {
      name: "College in the Schools",
      mascot: "",
    },
  }
  CAMPUS_LIKES_BY_ABBR.default = {
    name: "Unknown Campus",
    mascot: "Unknown Mascot",
  }

  def campus_name(abbreviation)
    CAMPUS_LIKES_BY_ABBR[abbreviation][:name]
  end

  def campus_mascot(abbreviation)
    CAMPUS_LIKES_BY_ABBR[abbreviation][:mascot]
  end
end

I am not very familiar with Ruby, but why couldn’t something like this work?

class CampusDetails
  private

  def build_campus(abbreviation)
    begin
      Object.const_get(abbreviation)
    rescue
      UnknownCampus
    end.new
  end
end