Skip to main content

Class 3: Ruby, continued

Held: Friday, 27 January 2017

We continue to investigate some issues in Ruby.



  • Reflections on exercises
  • Duck typing
  • Additional characteristics of Ruby
  • Meta discussion
  • Object-oriented programming in Ruby
  • Q&A


News / Etc.

  • Welcome to day three of CSC 321!
  • Today we conclude our exploration of Ruby and start on Rails.
  • Next week, we will mostly explore Rails.
  • We will have a visitor for the second half of class on Tuesday. Shu-Yang Lin, She will discuss design issues and more.
  • I’m still working on the course Web site.
  • It appears that RubyGems has some vulnerabilities I would suggest that you do your devleopment on Cloud 9, rather than on your personal computer.

Upcoming Work

Good things to do


  • NEW Rosenfield Internship Talks, Today at 11 a.m. in JRC 101.
  • NEW CS Extras today at 4:15 p.m.: Contracts
  • NEW Writers@Grinnell Reading, Today at 6 p.m. in the Pioneer Bookshop.
  • NEW Rosenfield symposium, next week. (Lots of different events)


  • ???

A brief introduction to Ruby

  • Modern programming language.
  • “One” designer.
  • Imperative, functional, and OOP characteristics.
  • Good at “Get the job done quickly.”
  • Very dynamic.
  • Very popular.
  • Everything (more or less) is an object.
  • Includes anonymous functions, although with a different syntax than we might expect.
  • Disadvantage: Too many ways to express the same concept.

      if TEST consequent
      consequent if TEST
      if TEST
      unless not TEST
      consequent unless not TEST

Some Ruby exercises

We will explore some of the examples from today’s assignment to see the different ways in which students approached problems.

Write sums_to_n?(vals,val) that returns true if any two distinct values from vals (a list of values) sums to val.

Write multiple_of_4?(bitstring) that takes a string of 0’s and 1’s (representing an unsigned integer) as input and returns true if the string represents an integer divisible by four.

Write starts_with_consonant?(str) that determines if a string starts with a consonant.

Additional characteristics of Ruby

What did you see as important characteristics of Ruby?