CSC302 2011S, Class 02: Ruby (1)

Overview:
* Summary of Ruby concepts.
* Typing.
* Lab.

Admin:
* I'm still negotiating how to deal with the reading questions.  Generally, I'll read them all to think about what to discuss, but won't cover everything.
* Disclaimer: I am not an expert in any of the languages we are discussing.  I certainly don't know about the underlying implementation details (although I can hypothesize a bit).
* If you really care about how something is implemented, you could make it the topic for your presentation.

* Reading questions due Thursday: Tate 2.3.
* HW 1 is due Thursday!

* EC for Microsoft Presentation, Thursday, 4:15 @ CDO.
* EC for "Waiting for Superman", Thursday, 7:00 @ Harris Cinema.
* No CS table this week

Things you've learned how to do in Ruby
* We can print strings with puts
* Tests can be combined with
  and, or, &&, ||, &, |
  * The last two don't do short-circuit evaluation: They keep evaluating
    until they reach the end
  * Why short circuit?
    * Efficiency.  Why do work that you don't need to do?
    * Safety: The second test might rely on the success of the first
      C programmers like to write things like if x && x->ok
    * Syntactic sugar: You could do without it, but it requires a lot
      more typing.
  * Why not short circuit?
    * So that people who don't understand short circuit evaluation can
      write code they can understand
    * If tests have side effects, you may want to ensure that all the
      side effects happen
* Conditional statements
* You can find out what methods are available for an object with
  object.methods
* Two kinds of strings: "Foo" and 'Foo'
   Strings in double quotes get evaluated

Random Questions
* Is 3 + 4 syntactic sugar for 3.add(4)?
  * Yes
 
Typing:
* Static
* Dynamic
* Strong
* Weak 
* Duck

Debrief

* How did you print your name ten times?
  10.times {puts "Andrew"}

* How did you print the ten sentences?
  x = 0
  while x < 10
    puts "This is sentence #{x}"
    x = x + 1
  end

  (0..9).each {|x| puts "This is sentence #{x}"}

* Why do languages commonly use zero-based indexing for arrays and strings?
  * It saves an operation in addressing

* Are blocks first-class objects?  How can you tell?  If they are not,
  why not?