CSC/ECE 517 Fall 2009/wiki2 7 cn

Problem Statement

Different languages have different mechanisms for "code reuse". Assembly and low level languages have macros, C/C++ has includes, Ruby has mixins and modules, Java has packages, and there are many other concepts around reuse and extension. Here is a page that describes the various mechanisms, groups the mechanisms into logical categories, and discusses the advantages and disadvantages of the various schemes, in terms of simplicity, performance, reliability, or other factors.

Code Reuse - A Brief Overview

Code reuse, also called software reuse, is the use of existing software, or software knowledge, to build new software. Code reuse in software development is something assumed literally through re-using bits of code in more than one place. It is truly achieved through using common libraries and interfaces accessible to both the entire application and to other applications in the domain. Here are some of the features of code reuse.

Reuse is not duplication

Duplicating code is the result of a copy-paste scenario. The moment you have copy-pasted a module of code to two locations in your application you’ve just created an additional maintenance point. Also if you have coded a bug into the original code & duplicated it in multiple locations, the bug has now been instantiated in more than one place. Reuse is different from duplication. In code reuse the logic or work that a module does in multiple areas of the application can be reused from one place.The code doesn’t have to physically reside in all of those places to get reused.

Interfaces

Reuse is not always functional code that needs to be applied in more than one place. It can be obtained through the use of interfaces and generics as well. By using a solid interface design to allow any type of object with a compatible set of methods to be used in a piece of your application, you allow for everything on both sides of that interface to be easily interchangeable. Other type of interface-like methods that promote architectural reuse are generics, tag libraries, and dozens of frameworks out there that allow pieces to be easily decoupled and injected into the application.

Advantages of Code Reuse

• Reusing code saves programming time, which reduces costs.
• Sharing code can help prevent bugs by reducing the amount of code that needs to be written to perform a task. The shared code can also be tested separately from the end applications.
• Separating code into common libraries lets programmers specialize in their particular strengths. A security library, for example, can be built by security experts while a user interface which uses the library can let UI experts focus on their tasks.
• Delegation of tasks into shared modules allows offloading of some functionality onto separate systems.

Drawbacks

• Maintenance nightmare – If for any reason one to make changes in the copied section, changes have to be made ALL the copies.
• Unorganized – Reused code tends to be unorganized .It may generate create massive amounts of code which is difficult to decipher after a while.

Examples of Effective Code Reuse

• Google Chrome is an excellent example of code reuse, it uses at least 25 different software Libraries.
• Matlab programs are also a good example of code reuse where one reuses different functions from the matlab tool box.

The Page now talks about reuse in different languages such as C, C++, Java & Ruby.

Code Reuse in C/C++

Functions

(Applicable for both C/C++) Instead of writing a same function multiple times, we can call the function, thus making the code more concise, readable & modular. Another way of using functions is to write them in header files & then including the header files in the code. Later the functions written in the Header File can be called directly from the main program.

Different Types of Header Files used in C/C++ are as follows:

• assert.h, math.h, string.h, stdio.h, time.h etc

Simple Program to Illustrate C Functions:

#include <stdio.h>
void print_message(void);
{
printf("Hello World \n");
}

Main Program

int main(void)
{
print_message();
return 0;
}

Classes

(Applicable only for C++)

References

http://www.refactoring.com
Refactoring: Improving the Design of Existing Code by Martin Fowler.

References

http://www.refactoring.com
Refactoring: Improving the Design of Existing Code by Martin Fowler.