Data Types, Expressions, Control Flow and Unit Tests

You will explore these topics with a partner.

Lesson: Data Types

Review: Ruby Data Types

On a piece of paper:

1. Write a line of Ruby code that illustrates that arrays are heterogeneous
2. Write a line of Java code that highlights the fact that Java arrays are homogeneous.
3. Write a line of code that illustrates that ArrayList in Java can be heterogeneous

Symbols are ubiquitous in Ruby, but can be confusing at first. Read:

• http://www.troubleshooters.com/codecorn/ruby/symbols.htm#_What_are_symbols
• http://www.randomhacks.net/2007/01/20/13-ways-of-looking-at-a-ruby-symbol/

Add to your paper:

1. Explain the statement “A Ruby symbol is an object with O(1) comparison”.
2. Name one common usage for a symbol

Do a quick Google-search to explore: How do Ruby’s symbol compare to C++ enums? to Java enums?

Lesson: Expressions

Review: Ruby Expressions. From the Ruby demo files you downloaded in the Intro exercise, take a look at ruby_expressions.rb.

Self Test

Explore, no need to record answers, but DO answer every question!

1. Does Ruby have overloaded operators? Is there any difference between puts a[0] and puts a.[](0)?
2. What is the effect of: a.[]=(0, 5)?
3. What is an lvalue?
4. How does parallel assigment work?
5. Are constants really constant in Ruby?
6. What does it mean to be right associative?
7. What is a programming idiom?
8. What is short-circuit evaluation?
9. What can you do with the splat?
10. In a Ruby program, you see the name whatever. How would Ruby decide whether this is a variable or a method?

Control Flow

Review: Ruby Control Flow. From the downloaded files, take a look at ruby_control_flow.rb.

Slides 1-11: Part of the popularity of Ruby stems from its expressive syntax. Review these slides and play with the code corresponding code, through the comment that says #yield.

Add to your paper:

• Slide 12 asks you to trace the code on the following slides
• Be ready to discuss with the class when/why yield might be useful
• Do the in-class challenge on slide 14
• We’ll explore blocks in more detail (slide 15) later

Ruby Unit Tests

On your own (not an in-class exercise).

The concept of unit tests is the same as other languages. Review Ruby Unit Tests. From the downloaded files, take a look at ruby_unit_test.rb. The only self-test is to be sure you understand why we need assert_in_delta rather than just assert_equal.

Note: The hardest part of using Ruby unit tests is that the syntax changed after Ruby 1.8. Be sure you have installed a later version of Ruby. Be sure that the tests really run. You’ll practice this in the Ruby Basics homework. If you have issues, submit questions on Piazza.

Submit/Rubric

No submission. Keep your answers as a study guide.