CSC/ECE 517 Fall 2009/wiki2 8 RP

Reflection Oriented Programming

---

Definition

Reflection is a process of reasoning about and acting up on by itself [1]. Throwing more clarity we can presume reflection as a computer code which can be dynamically modified in the process of execution. The dynamic modification depends on the code features and its run time behavior.A system which exhibits such reflective behavior is called as reflection oriented system.

Overview

This Article throws light up on what Reflection Oriented programme is about. It deals with the need for such dynamic aspect and how it is useful in satisfying the practical needs.Further it highlights the research work that is carried out in this area and scope for future improvements.

Reflection oriented programming – Insights

Reflection

Reflection is the process of converting a programmatically expressed value into a component of interpreter state [2]. In the case of usual programs the information about itself (i.e the program) is lost as soon as it finishes compilation ,but in Reflection the program (object) needs to have information about its structures. This is done by storing it in the form of metadata[3].

There are two types of reflection based on its dynamic nature.Few programs support reflection during compilation. They are called as compile time or static reflection. Runtime reflections are those which are carried on during runtime and its the usual form of reflections.

Example of Reflections:

A simple ruby code does enough to understand the concept behind reflections

puts 12.kind_of?

The above code dynamically finds out what kind is 12 ? It returns the value integer. Thus reflection is done in ruby code to carry out operations during runtime with metaprogramming[4] enabled.

Reflection Oriented Program as Paradigm

Reflection oriented paradigm is a new paradigm used as an extension to the object oriented paradigm. It adds various features meeting the need of various applications and its very flexible. Its a dynamic run time paradigm unlike object oriented and procedure oriented model. In this paradigm objects can be varied and modified according to the needs during the run time rather than creating static set of codes with a predetermined set of operations.

The dynamic decision in this paradigm is decided based up on the data being processed and the manipulation performed on those data sets.Here is where the knowledge about its own structure plays a crucial role. On considering an example wherein a program needs to change dynamically on various sets of data (find an instance of that data or length) ,intercepting the interpreters becomes important. In these cases the program should consist of codes just to identify the data and to decide the operations to be performed on them.

Concepts

The concept of reflection oriented programming is based up on the extension of object oriented program to dynamically shape the program based on its data. All the computations can be divided in to two categories.ATOMIC and COMPOUND.Atomic refers to when the computation is completed in a single logical step whereas compound refers to the computation that requires the completion of sub computation

To make the concept work as described earlier a new entity called metainformation(information about information) is introduced.It takes into account of the details contained in the meta level.It acts as a storage wherein it contains the metainformation. It changes as the state changes and its designed to hold the metainformation of the current state.On encountering data it derives the information of the state, processes it and triggers the state change. These operations are performed during runtime

Reflectives

A reflective does the job of describing the behavior of metainformation. The current state of meta information is reflected by the instances of reflectives or objects of reflectives. Reflectives can be broadly classified in to two catgories. Simple reflective and Control reflective.Simple reflective contains the computational concepts whereas Control reflectives contains concept related to flow and control.

There is a subcategory of simple reflectives that is designed to contain the meanings of the expressed values. Its called as value reflectives. The common notation for expressing relative is <reflective>.Numerous examples of reflectives can be found here [5]

Examples and Scenerios

Below is an example for reflection in ruby. Here the class person has a function defined which is used to display the name. An object is created to the class Person and we use obj.send to send the object to the function. This shows the dynamic behavior in ruby

class Person 
 def greet (name)
  puts "hello, #{name}"
 end
end

p = Person.new 
p.send(:greet, "Sam")