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Language of the Month
If it’s December, it must be Ruby!
Adam Coffman and Brent Beer
Ruby – An Overview
 Ruby is a multi-paradigm programming language
designed for ease of use and programmer happiness
 Ruby borrows concepts from scripting languages like perl,
object oriented languages like SmallTalk, and functional
languages like Lisp
 Ruby was created by Yukihiro “matz” Matsumoto in 1995
in Japan
 “Often people, especially computer engineers, focus on
the machines. They think, "By doing this, the machine will
run faster. By doing this, the machine will run more
effectively. By doing this, the machine will something
something something." They are focusing on machines.
But in fact we need to focus on humans, on how humans
care about doing programming or operating the
application of the machines. We are the masters. They
are the slaves.” -Matz
Ruby – An Overview cont’d
 Ruby is an interpreted language rather than a
compiled one.
 Ruby has an interactive, real-time shell: IRB
(interactive ruby)
 Ruby features single inheritance only.
 Ruby favors blocks and closures over traditional
Coming from C++
 If you already know C++ you know many of the
important concepts Ruby utilizes
 Classes, methods, loops, conditionals.
 Most standard operators
 OO ideas
 You probably don’t know
 Blocks
 Duck typing
 Dynamic Programming
A Comparison: C++
A Comparison: Ruby
What do you notice?
Variable Scope Using Sigils
 The sigils $, @, @@ are used in ruby to denote
variable scope.
 $ denotes a Global variable
 @ denotes an instance variable
 @@ denotes a class variable
 <^> denotes a sombrero, often worn by Darth Vader
Everything is an object!
If we tried something like this in C++ or Java:
It fails.
This is because in C++ or Java, numbers and Strings are not Objects.
As such, they cannot posses methods or attributes.
Everything is an Object
 In Ruby those would be perfectly valid operations
 This is because, like SmallTalk, Ruby is a purely
Object Oriented language. Numbers, Strings, and
Characters are all Objects.
 When they say everything is an Object, they
mean it!
Ruby Operators
 Many operators you will be familiar with from C++
 +, - , / , = , == , [ ], !
 Many you may not be
 { }, =~, *, **, ..
Dynamic (Duck) Typing
 No need to declare variable, argument, or return
 If it looks like a duck, walks like a duck, and quacks
like a duck….it probably is a duck
Hashes / Arrays
 Ruby has two basic data structures: Hashes and
 Arrays are denoted by [ ] while Hashes are
denoted by { }
 Both use the Enumerable mixin, and thus have
access to iterator blocks such as inject, map,
each, and reject.
 Hashes use key value pairs in much the same
way traditional Arrays use indices. myHash[key]
returns key=>value.
 Blocks are a concept Ruby borrows from
functional programming languages.
 In Ruby, blocks are usually used in place of
traditional loops.
 Let’s look at two common types of blocks: each
and map.
Just How Dynamic is Ruby?
 A class is never finalized in Ruby, even system
 It is never too late to open up a class and
change it.
 For instance, maybe we think that the Array class
could use a sum method, adding it is trivial.
 Metaprogramming is writing code that writes
 Ruby’s dynamic nature lends itself to
 We have actually already seen a built in
example of Ruby metaprogramming in the form
of attr_accessor.
 Lets look at two more examples: virtual functions
and “n_times”
Virtual Functions
 Ruby has no built in functionality for
implementing C++ style virtual functions (with a
dynamic language, there are better solutions).
 However, using metaprogramming, adding such
functionality is trivial if you wanted to.
 def self.something defines a Class method
 The following code defines 10 methods.
What isnt’t Ruby?
 Ruby isn’t fast yet. Its current implementation is
the slowest of the major scripting languages
(perl, python etc)
 The newest version of Ruby (1.9) is in progress and
so far tests faster than perl or python.
 There are several third party Ruby interpreters in
development with even faster speeds. MagLev is
one of the most promising.