CSC/ECE 517 Fall 2009/wiki1a 11 AS

Definition of Ruby and Python

Ruby is a dynamic, reflective, general purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features.

Python is an interpreted, object-oriented, high-level programming language with dynamic semantics.

Differences in their language features

The first thing to be noted in Ruby is that in Ruby everything is an object, whereas in Python you have the liberty to code without using objects.

// include example here

In ruby, the programmer can use blocks to extend the language for application specific control statements where as in Python you are supposed to use only the control statements provided by the language.

Differences in Programming Environment

Python has a Virtual Machine which optimizes certain functions like hash functions and sorting algorithms.

Ruby as such does not have any virtual machine but it acts as an interpreter. There is a project going on for building a virtual machine for Ruby- YARV [1]

What Ruby has and Python does not have?

Ruby has continuations, where as Python does not have it. One notable use of continuations in Ruby is for breakpoints in debuggers. Continuation is an abstract representation of the control state, of the things to come. Practically continuation support in a language means we can “save” our state at a point and return to it later. This is called a first-class continuation.

In ruby, the callcc method is used (it’s Kernel#callcc) to create a Continuation class. Look at this small sample:

def loop
  cont=nil
  for i in 1..4
    puts i
    callcc {|continuation| cont=continuation} if i==2
  end
  return cont
end
c = loop
c.call

In irb this will print 1,2,3,4 then 3,4 again, then exit. As a script file run by the main ruby interpreter, this will loop forerver as it captures the control state of the program when and where it was called and this includes returning the continuation and then calling it again.

What Python has and Ruby does not have?

It’s worth mentioning that Python has some big features like list comprehensions that Ruby doesn’t.

 [foo(x) for x in alist if bar(x) != 'frotz']

This is definitely shorter than:

  foo = [] 
  for x in alist:
  if bar(x) != 'frotz':
  foo.append(x)

Advantages over statically typed languages

1.Java has static typing. We declare the type of each variable, and then, during compilation, we get an error message if we use a variable of the wrong type. Ruby, on the other hand, has dynamic typing: We don't declare types for variables or functions, and no type-check occurs until runtime, when we get an error if we call a method that doesn't exist. Even then, Ruby doesn't care about an object's class, just whether it has a method of the name used in the method call. For this reason, the dynamic approach has earned the name duck typing: "If it walks like a duck and quacks like a duck, it's a duck."

Duck Typing

class ADuck
    def quack()
        puts "quack A";
    end
end
class BDuck
    def quack()
        puts "quack B";
    end
end
# quack_it doesn't care about the type of the argument duck, as long
# as it has a method called quack. Classes A and B have no
# inheritance relationship.
def quack_it(duck)
    duck.quack
end
a = ADuck.new
b = BDuck.new
quack_it(a)
quack_it(b)

2.In Ruby, variables do not need to be declared and are free to change type from statement to statement. So the following code, where the variable x changes from a FixNum (an integer that fits within a native machine word) to a String to an Array, is a perfectly legal sequence of Ruby code:

x = 10
x += 4
x = "My String"
x = [1, "My String", Hash.new ]

3.Ruby's dynamic typing means you don't repeat yourself: In Java have we had to suffer through verbose code along the lines of

 XMLPersistence xmlPersistence = (XMLPersistence)persistenceManager.getPersistence(); 

Ruby eliminates the need for the type declaration and casting (as well as parentheses and semicolon): a typical Ruby equivalent would be

 xmlPersistence = persistence_manager.persistence.

4.In Java, we often iterate over a collection's Iterator, running the logic on each element. But the iteration is just an implementation detail: in general, we are just trying to apply the same logic to each element of a collection. In Ruby, we pass a code block to a method that does just that, iterating behind the scenes. For example,

 [1, 2, 3, 4, 5].each{|n| print n*n, " "} 

prints the string 1 4 9 16 25; an iterator takes each element of the list and passes it into the code block as the variable n.

Projects better suited for Ruby

The most prominent application of Ruby is in web development using Ruby on Rails. Ruby on Rails is an open source web framework. Rails was created by David Heinemeier Hansson in 2003. Since then many applications have been created using Ruby on Rails and presently this has been used in various applications like twitter [2] e-commerce[3], live video streaming [4], group chat application [5].

Projects better suited for Python

Python has two web development frameworks: Django and TurboGears. Apart from web development, Python also provides platform for applications like Database Access, Desktop Graphical User Interface(GUI) development, Software development, Game and 3D graphics development. One of the best examples of open source Python language is the "Zone Application server" [6].