Constantize to the Rescue!

The Problem and First Approach

I recently came across an interesting problem. I had a couple of classes Teacher and Student. Both classes had a method called .login that brings you to their respective login screens. While it may be inefficient, the user type is inputted by the user through a gets method.

user = gets.strip   # where user equals "Teacher" or "Student"

We either want to call Teacher.login or Student.login based on whichever option is submitted through the input. We can do this with an if/elsif statement like this:

if user == "Teacher"
   Teacher.login
elsif user == "Student"
   Student.login
end

That can get pretty inefficient with the more user types added and can result in an extraneous amount of code.

So, I figured it would be most efficient if we tried to execute something along the lines of user.login, where user is the class name we’re trying to access. While it looks like it should work, it doesn’t. We get an error —

undefined method `login’ for “Student”:String

Being that I was only recently introduced to Ruby at the time, I was perplexed as to why I kept receiving this error.

After some research, I discovered object types in Ruby. There are a bunch of different object types such as a string, integer, boolean, etc. So what type of object is Student or Teacher? To find the target object type that we need user to be, I ran Student.class and that returned Class. So, if we want user.login to work, we need to get user to be a Class object type and not a String.

Ruby’s constantize method provides a really efficient way to solve the problem at hand. user.constantize turns user into an object type of Class and thus the final code works:

user.constantize.login

This shortens our original code significantly, especially when we are operating with more that two user types.