CSC/ECE 517 Fall 2012/Table Of Contents

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Introduction

This wiki page will give you the outline of the topics from Wiki 1a and 1b. A brief introduction to the topics covered(in 1a and 1b) and the links to the appropriate topic is available on this page.

Object Oriented Programming

Object-oriented programming (OOP) is a programming language model organized around "objects" rather than "actions" and data rather than logic. An introduction to Object Oriented Programming and its primary concepts like abstraction,polymorphism,encapsulation and inheritance are explained here.Features and advantages of Object oriented programming is given here. Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. Functional programming decomposes a problem into a set of functions.It is the opposite of object oriented Programming. Advantages of functional programming are given here. We can perform functional programming on an object-oriented programming language because of the following reasons:

  • Object can have constant state.
  • Method can depend only on its arguments and context available at method definition time.

Combining both of these paradigms will not only provide us a robust design structure, but also will enable the programmers to develop solutions to complex problems quickly and effectively.More details can be found here.

Some of the basic features of Functional Programming which can be combined with Object Oriented paradigm are:

A number of programming languages support mixing of both functional and object-oriented code. Three of these (Scala, Ruby, and Conjure), are described in more detail here.

Multiple Inheritance is one of the features of a few Object-oriented (OO) languages in which a class inherits properties (variables & methods) from more than one parent class . The former is called a sub or child class and the latter is called a super class or ancestor class. Here are the usage guidelines of multiple inheritance.A real world example of multiple inheritance is given here. C++ supports multiple inheritance. A detailed explantion is given here. JAVA doesn't support multiple inheritance but with the use of the concept called interface, multiple inheritance can be simulated. A more detailed explanation is available here. Ruby doesn't support multiple inheritance but provides a similar feature using modules and mixins. Advantages of Mixins are given here. Object oriented languages support inheritance through different mechanisms. Methods from parent classes can be re-implemented in child classes to improve the behavior of the child class without having to re-write the whole class or define a completely new method. As method re-implementation in descendant classes is achieved differently in different classes it is crucial to understand these mechanisms. A brief explanation of Multiple inheritance in Scala and Python is given here. Advantages and disadvantages of Multiple inheritance are given here. Because of few drawbacks(which are discussed above), few languages have implemented concepts like Modules and Mixins to emulate the power of multiple inheritance. Multiple Inheritance is supported by several object oriented languages such as C++, Ruby, Perl, Python etc.Implementation of multiple inheritance in each of these languages is compared here.

The Object-Oriented programming paradigm has two ways for specifying objects,Set based language - object specification and Protocol based language - object specification.

Ruby

Ruby is a dynamic, reflective, object oriented programming language which was first developed in mid 90s by Yukihiro "Matz" Matsumoto in Japan.[1]. It is a cross plat-form interpreted and object-oriented language. It is designed for the principle of least surprise. Matz says "I wanted to minimize my frustration during programming, so I want to minimize my effort in programming. That was my primary goal in designing Ruby. I want to have fun in programming myself. After releasing Ruby and many people around the world got to know Ruby, they said they feel the way I feel. They came up with the phrase the principle of least surprise."[2] In 2004, web application framework of Ruby "Ruby on Rails" was introduced by David Heinemeier Hansson. With increased complexity of codes, it became essential to design a development environment which will include some intelligence in code writing with increased version control and simpler debugging. Popular IDEs for Ruby are RadRails,Netbeans,Textmate,Rubymine,jRuby and RDT. A brief outline is given on objects,classes and inheritance.Ruby can act as a set-based language and prototype-based language.

A Method is a Subroutine (or Procedure or Function) in a class that defines the behaviour exhibited by the associated Class instances at runtime. Methods defined within a Class are bound to the class either by Static binding or Dynamic binding. An example of a method in Ruby is given here.Instance methods,static methods,accessor methods are different kinds of methods. A closure is basically a method/function that has the following two properties:

  • We can pass it around like an object (to be called later)
  • It remembers the values of all the variables that were in scope<ref>http://en.wikipedia.org/wiki/Scope_(computer_science)</ref> when the function was created. It is then able to access those variables when it is called even though they may no longer be in scope.Closures must be explicitly supported by the language. In order for the language to be able to support closures, it must support first-class functions.

A normal function is defined in a particular scope (i.e. in a class) and can only be called within that scope. This function has access to all the variables in the scope that it is defined, like the parameters that are passed into it as well as class variables. A closure on the other hand may be defined in one scope and be called in a completely different scope (since we can pass it around before calling it). Because of this, when a closure is created, it retains the values of all the variables that were in scope when the closure was defined. Even if the variables are generally no longer in scope when the closure is called, within the closure they still are. In other words, the closure retains knowledge of its lexical environment at the time it was defined. Examples of closures are given here. Instance variables in ruby are defined.Advantages of closures are given here. Class variables and class methods in Ruby are defined here.The basic syntax to declare them as class variables and instance variables is also given. Ruby Modules are similar to classes in that they hold a collection of methods,constants and other module and class definitions.Modules definition is similar to classes just that we use the keyword module instead of the class keyword.Unlike classes, objects cannot be created based on modules nor can it be sub classed.However, it can be specified that the functionality of one module should be added to another class, or a specific object. Uses and examples of modules are given here. The most interesting fact about the use of modules is to define mixins. When a module is included within a class,all its functionality becomes available to the class.Modules can contain class methods and instance methods. Mixins are different from #include and multiple inheritance and this is demonstrated here. More about Mixins can be found here.

Namespace in C++ is similar to modulesIn general, a namespace is a container for a set of identifiers (names), and allows the disambiguation of homonym identifiers residing in different namespaces.Namespace usually group names based on their functionality. Usage of namespaces and its example is given here. Multiple inheritance in C++ similar to mixins.You can derive a class from any number of base classes. Deriving a class from more than one direct base class is called multiple inheritance. An example is given here. Interfaces in JAVA is similar to mixins.A Java interface defines a set of methods but does not implement them.A class that implements the interface agrees to implement all of the methods defined in the interface, thereby agreeing to certain behavior, thereby implementing multiple inheritance. Properties of an interface are:

  • An interface is implicitly abstract. You do not need to use the abstract keyword when declaring an interface.
  • Each method in an interface is also implicitly abstract, so the abstract keyword is not needed.
  • Methods in an interface are implicitly public.

An example is given over here.Comparison between mixins and interfaces and given here. Comparable and Enumerable are commonly used mixins.

Ruby has simplified the way programmers use loops and iterators. Ruby helps programmers to use Don't Repeat Yourself (DRY) principle effectively by using blocks and defining iterators over collections.<ref name="Iterators">Alan Skorkin. "A wealth of ruby loops and iterators" http://www.skorks.com/2009/09/a-wealth-of-ruby-loops-and-iterators</ref> This helps in minimizing the development work that programmers often find in any other O-O style programming language. In ruby, these iterators, blocks and functional idioms are explained as:

Iterators are Collection defined methods that helps to iterate over all the elements present in a Collection.<ref name ="tutorial_point_i">"Ruby Iterators" http://www.tutorialspoint.com/ruby/ruby_iterators.htm</ref> Ruby Collections are basically objects that store a group of data members of various types. Examples of Collection are arrays, hashes etc.
A block consists of chunks of codes with a name assigned to it.<ref name="blocks">"Ruby blocks" http://www.tutorialspoint.com/ruby/ruby_blocks.htm</ref> For example, 

  my_block { puts "Hello World" }

Different types of iterators in Ruby are times iterator,upto iterator,step iterator,each iterator,collect iterator,map iterator. Ruby allows programmers to define their own iterator other than the iterators listed above. For example if a programmer wishes to define an iterator which prints an array in reverse order, then he can do so as shown here. Blocks are the most commonly used form of closures in Ruby. We can find them all over the core Ruby libraries. They are nameless functions and can be passed anywhere.A Block consists of a chunk of codes with a name assigned to it.Alternately, a block is a code which is passed to the iterator. These blocks can either be defined by enclosing them in curly braces or by using the do...end syntax as shown here. Procs are nameless block of code that can be represented as an object and can be passed around or called at will.Lambdas are a more strict form of proc.

Multiple Inheritance has several disadvantages that can lead to ambiguous code behavior either during compile time or run time.Ruby does not support directMultiple Inheritance. But, Multiple Inheritance can be achieved in Ruby through Modules. Modules simulate multiple inheritance in Ruby.Given here is the Taggable-string example taken from the Class notes of CSC517, NCSU. Suppose we want to add tags to Strings, we can define a Taggable module and include it into the class. Multiple inheritance may cause name conflicts when a sub-class inherits different super-classes that contain the methods or variables with the same name. This can be resolved in many ways. Advantages and disadvantages of multiple inheritance are given here.


Expression orientation<ref name="saas_video">"SaaS. 3.6 - Ruby Blocks, Iterators, Functional Idioms " http://www.youtube.com/watch?v=bRn91_Zonh4</ref> in ruby refers to the mechanism of applying a series of operation on collections ( e.g. arrays, hashes etc ) without actually modifying the original collection. For example, consider the sort method in ruby. The sort method when called on an array creates a temporary array having the same elements as that of the original array. It then sorts this temporary array and returns that.

Functional idioms refers to the various constructs in ruby that mimics [Functional Programming Language Functional Programming Language. Most programmers argue that Ruby is actually an Object Oriented Programming Language and it does not behaves as per the functional programming paradigm.

Regular expressions are extremely powerful.Rubywas built as a better Perl hence it supports regular expressions.Regular expression is sort of a string used to match to other strings.In ruby regular expressions are written in the format /pattern/modifiers where pattern is the regular expression and modifiers are the series of characters specifying the various options. More on regular expressions can be found here.

Redirection refers to redirection of incoming request from one page to another. HTTP is stateless, hence redirection with session/flash makes it stateful.As the http requests are stateless,it leads to losing the state of the previous request. Thus Rails provides hash called Flash which persist until the end of the next request received and Session hash, which unlike flash persists forever. The working,example,advantages and disadvantages of flash/session is given here.

Code Reuse

Code reuse, also known as software reuse is the practice of using the same segment of code in multiple applications. The definition, overview and a brief history of code reuse is found here. There are several techniques in code reuse. Code can be reused by using simple coding. For example, using a single line of code, we can reuse the code.Procedures and macros are the low level code reuse techniques.Methods can be used in code reuse, a method can be defined and declared multiple times wherever required. An individual software component is a software package, a Web service, or a module that encapsulates a set of related functions. All system processes are placed into separate components so that all of the data and functions inside each component are semantically related. Because of this principle, it is often said that components are modular and cohesive. With the help of Packages,modules and inheritance, we can achieve code reuse. Generators,Software architectures, code scavenging, Transformational systems, Very High Level Languages (VHLL) are more techniques of code reuse. Here are some of the best practices to be followed to make sure that the code that is being written is reusable. Advantages and disadvantages of code reuse can be found here. Here are few of the tradeoffs for code reuse at various levels of components.

Reflection

Reflection is a relatively common computer programming concept where in the program has the inherent ability to examine itself at run time. Based on its observations the program can modify it's behavior for the given situation.The modifications can be any aspect of the programming language .i.e syntax, semantics, or implementation. Precisely, "Reflection" can be defined as a language's ability to inspect and dynamically call classes, methods, attributes, etc. at runtime. More advanced uses of reflection let you list and call methods, constructors, etc. A little more introduction about reflection is found here. There are many challenges faced by designers of reflective languages. They must provide as much leeway as possible for late binging and at the same time they must optimize the compilation of the static components so that they are ready for run-time. Reflection is in essense a connection between the object-level (program) and meta-level (the processor). The ability of the object level to be able to observe and modify the meta-level information is the consequence of this connection. These actions can be termed as introspection (This involves the action of observing the class) and intercession (this involves the operation of modifying the behavior of the class). These actions can implemented with the implementation of the following components:

  • Ability to convert a string that denotes a class or a method into its corresponding reference or invocation.
  • Ability to use and create symbolic links to methods and classes.

There are two basic types of reflection. They are:

Features,advantages,disadvantages of reflection in C#,JAVA,Ruby,Smalltalk,PHP is given [expertiza.csc.ncsu.edu/wiki/index.php/CSC/ECE_517_Fall_2012/ch1b_1w40_ar#Structural_Reflection here]. Applications of reflection are given here. Comparison of reflection in different languages is given here. Advantages and disadvantages of reflection are given here.

References

http://en.wikipedia.org/wiki/Component-based_software_engineering http://en.wikipedia.org/wiki/Functional_programming http://docs.python.org/dev/howto/functional.html http://searchsoa.techtarget.com/definition/object-oriented-programming

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