I'm about to start coding a new website. My problem is that I'm still stuck in using old school coding methods.
I recently downloaded some open source code from Question2Answer.org and was really intrigued in how it was set out.
Does anyone know of any sources? or something that I could possibly download, a template or example to help me get started with a new site?
The site won't be anything fancy but I want to start moving into Web 2.0 and OO programming.
In short I want to do it right. Any advice would be appreciated.
It seems like this question isn't getting many answers, so I'll try my hand at it (even though I'd recommend a different language, just because PHP is such a terrible language ). PHP was the first language I ever wrote anything big in, and the one thing that I wish I had known at the time was the MVC design pattern. It has some advantages like:
Separation of logic and UI means less ad-hoc code, more functions (try to follow the "each function does one thing" rule -- It makes things much easier when you go back and look at code)
Functions are easier to verify correctness than huge function-less pages
Functions can be unit tested (do this!)
It's easier to figure out where things are (database logic is in one file, HTML in another, and "controller" logic in another)
Here's a pretty good high-level intro to MVC.
Key points:
The model talks to the database (or whatever other storage you're using).
The view displays things (HTML)
The controller does everything else
I found two good-looking PHP MVC tutorials here and here. Hopefully they're not too complicated, and feel free to ask more questions if anything doesn't make sense.
Good luck!
PS - Don't forget the point about unit tests! If you can't find a way to unit test a function, it's probably too complicated.
There is a reason why people chose PHP as a server-side scripting language. It's extremely easy to pick up and offers many different coding options. Many functions are included without having to know prior importing, and you do NOT have to write OO code if you don't want to.
This all leads to a huge downfall as well, because there are less restrictions on the structure of the code, it's much easier to write bad code.
I suggest using a framework. It saves you time, energy, and the opportunity to write bad code:
CakePHP is a rapid development framework for PHP that provides an extensible architecture for developing, maintaining, and deploying applications. Using commonly known design patterns like MVC and ORM within the convention over configuration paradigm, CakePHP reduces development costs and helps developers write less code.
http://cakephp.org/
http://www.phpframeworks.com/
IMO MVC ( and this OOP ) is nothing really fancy. It's basically a function to register a pointer to a function in an array for example like a hook. This array is looked by another function to do some stuff. A good MVC should have a callback function. IMO this OOP thing is more a bussines logic to help you to monetize your application. It's not really something difficult to understand.
In most discussions of OOP it's said that the advantage is re-usability.. You put in some extra work to define your classes, and it saves you time later in being able to create many instances and extensions of those objects.
A corrolary of this seems to be that you shouldn't switch from procedural to OOP programming until the tradeoff of writing up everything into objects is equivelant to the time you'll save.
In general, when is a good time to switch from procedural to OOP programming? Are there any signs/characteristics you generally look for to know your project needs to make that switch?
I'm assuming this question is from the standpoint/paradigm of being a beginner. Once a programmer has experience writing object-oriented code, you can certainly author a project from the beginning using this architecture. In fact, I'd argue that a top-down approach can save you huge amounts of time on larger projects.
For the bottom-up scenario you outline, though, I'd say you'd have to feel it out. Reference this wikipedia article for more information about the different approaches, generically speaking.
Specific to PHP, I'd say you could use this approach for a migration:
Take as much code as you can (ie:
related functions) and place them
into include files.
Create a container class for that file. You can start with just using all the functions by calling them in a static manner, or even using a static (singleton) class.
Gradually convert to an instance paradigm instead of the global data / static function one that is the badness of procedural programming.
This process is a great way to learn the ins and outs of OO, and in the end you will see the benefits. It will also teach you my initial point: that it takes a lot longer to convert something into OO than it does to start with a semblance of good (high-order) design from the beginning.
If it's not a very very simple application, now is the time. In fact, it's arguable that you should always program OOly, because it will be harder when you want to extend your program in the future.
I think it depends on the context. For graphics applications using an existing OOP framework, the tradeoff is instantaneous -- you'd have to go out of your way to write procedural GUI code in some contexts.
However, if you're doing raw data processing and not interoperating with any OOP framework, maybe you'd find that OOP never makes sense.
It may be very time-consuming to switch to OOP withing a project. I doubt it would be profitable, because it requires a lot of coding, a hell of a lot of testing, and then a LOT of refactoring. The whole concept of OOP is different from PP.
So I would recommend not to switch within the project, but start using OOP for new projects as soon as possible. When you feel comfortable, you can start thinking of an OOP design for your existing project(s) and gradually implement features in OOP. It will be a lot of work, though, and it will probably feel like rewriting the entire project.
I would look elsewhere for signs you need to switch. For all the hype--and I'm a big supporter of OOP--code reuse is often only marginally better with OOP languages.
OOP is simple another tool to help organize your code, like functions in the past. It's a great and useful tool. But the main benefits are making it easier to write and maintain your code.
If it were me and moving to OOP required almost a complete rewrite, I'd hold off until some more material benefits of the switch became apparent. If your code works, I don't know why you'd rewrite it.
It depends on the task, but having done both, here's what I would think about:
do you feel the work requires modularity? the ability to manage similar or dissimilar things from a central place? are there many repeating elements? will quick development or administration changes be important?
do you feel the problem you are attacking is predictable and repetitive? is the task best served by following steps to solve or by applying algorithms?
If more like 1, then go for OOP, otherwise if it's more like 2, then go for a procedure approach.
When in doubt, use what you're comfortable with.
It is rarely a good thing to change the programming style of an ongoing project.
You can always apply OO principles to procedural code if you want more clear-cut responsabilities among your entities.
check for instance this very interesting book on OO coding in ANSI-C
I have been writing a lot of code for work in PHP/MySQL. So far it has all been procedural making use of functions for functionality occuring multiple times/places. Starting to find some of the site hard to manage - time to go OO.
I want to learn about MVC with object oriented PHP & MySQL. I have some experience in Java and MVC but never anything to do with web technologies, i.e. HTML/CSS/JS etc. I don't really understand how the dynamically generated HTML fits in with the classes etc.
I am after some recommndations about where I can start. Ideally some sites with great examples from the ground up. I don't really want to use a framework at this point because I find that it does too much for you. Once I understand the OO approach with MVC I'll probably use a framework to managei easier.
Cheers,
Evan
You have a lot of code, and despite being hard to change, it probably works. Making an overhaul is going to set you back a while, so the best approach is incremental. Find some ONE thing that would seriously benefit from using objects, and use objects there. Refactor as you are able to run tests. You can work this in with the ordinary flow of events, and things work out OK.
Frankly, if you're serious about removing redundancy and duplication, you'll often find places where just writing a small function can make a dent. If you do this often enough, you'll find groups of functions that work on the same data. That will suggest where to look for objects.
In other words, if you listen with the right kind of ears, the code will tell you.
If you just want a good online course, maybe you should have a look at
http://www.lynda.com/home/DisplayCourse.aspx?lpk2=653&srchtrk=index%3A1%0Alinktypeid%3A2%0Aq%3APHP%20Object%20Oriented%0Apage%3A1%0As%3Arelevance%0Asa%3Atrue%0Aproducttypeid%3A2%0Acategory_facet%3APHP
This course was really useful for a friend of me. The progress he booked when he finished this tutorial was really great. It takes you through the basics of building a CMS in PHP and object oriented.
I think you should start with small pieces to get into OOP step by step. I mean that you should write simple classes for things you use often like handling forms, image uploads, site messages, session handling.
When you get used to programming classes and working on objects it will be time to jump for something bigger like refactor whole "engine" to OOP using mvc and other stuff.
Not really an answer but too big to be a comment.
Actually HTML has nothing to so with classes and JS and CSS has nothing to do with PHP, MVC and OOP at all.
Your code should produce some data which is going to be displayed one or another way. You can use some class to render this data, but it's not that important class.
While JS and CSS are totally separate files usually, called by browser directly from the server, avoiding your application code (unless being generated dynamically). Anyway you should have not too much concern in it.
Although it's still hard and non-trivial task to tie classes hierarchy with such a discrete way of execution of a typical PHP application. Once wise man have said once, "If Windows were have to restart after each user's click, it were written completely different".
welcome to SO.
I am by no means a PHP expert, here is my thought comes on top of my head:
OO programming with PHP does help, but not very likely as the rescue to removing all the redundancies or making your code "neater". The traditional way of coding in PHP can produce nice code. OO helps to encapsulate your code to hide the implementation and reuse others' code by direct composition and/or via inheritance.
I would say the real concern here is how to decouple the "static" html from the "dynamic" PHP.
For instance, there shouldn't be many :
echo "<h1>A title</h1";
echo "<p>blah blah blah...";
Even in conditional printing.
I would say separate the whole business logic on one page/script into several functions, and at least hide the nitty-gritty inside a function.
For your questions on popular OO frameworks of PHP, CakePHP is a good one, got its inspiration from Ruby on Rails.
Read MVC Tutorial in PHP to understand what MVC is then start using a MVC Framework like Zend, CakePHP, Symphony or CodeIgniter...
I'm hoping to get some tips to kinda help me break out of what i consider after all these years a bad habit of procedural programming. Every time i attempt to do a project in OOP i end up eventually reverting to procedural. I guess i'm not completely convinced with OOP (even though i think i've heard everything good about it!).
So i guess any good practical examples of common programming tasks that i often carry out such as user authentication/management, data parsing, CMS/Blogging/eComs are the kinda of things i do often, yet i haven't been able to get my head around how to do them in OOP and away from procedural, especially as the systems i build tend to work and work well.
One thing i can see as a downfall to my development, is that i do reuse my code often, and it often needs more rewrites and improvement, but i sometimes consider this as a natural evolution of my software development.
Yet i want to change! to my fellow programmers, help :) any tips on how i can break out of this nasty habbit?
What is the point in using object-oriented programming when you cannot find good reasons or motivation to do so?
You must be motivated by the need to conceive and manipulate ideas as objects. There are people who feel the need to be perceptive of concepts, flow or functions rather than objects and they are then motivated towards programming oriented towards concepts, ideas, or functional flow.
Some 13 years ago, I switched to c++ from c simply because there were ideas I needed but c would not easily perform. In short, my need motivated my programming oriented towards objects.
The object-oriented mind-set
First, you have bytes, chars, integers and floats.
Then your programme starts being cluttered with all kinds of variables, local and static.
Then you decide to group them into structs because you figured that all the variables which are commonly passed around.
Conglomeration of data
So like printer's info should have all its variables enclosed into the Printer struct:
{id, name, location,
impactType(laser|inkjet|ribbon),
manufacturer, networkAddr},
etc.
So that now, when you call function after function over printer info, you don't have functions with a long list of arguments or a large collection of static variables with huge possibilities of cross-talk.
Incorporation of information
But data conglomeration is not good enough. I still have to depend on a bunch of functions to process the data. Therefore, I had a smart idea or incorporating function pointers into the Printer struct.
{id, name, location,
impactType(laser|inkjet|ribbon),
manufacturer, networkAddr,
*print(struct printer),
*clean(struct printer)
}
Data graduates into information when data contains the processes on how to treat/perceive the data.
Quantization of information
Now laser, ribbon and inkjet printers do not all have the same set of information but they all have a most common set of denominators (LCD) in information:
Info common to any printer: id, name, location, etc
Info found only in ribbon printers: usedCycles, ribbon(fabric|cellophane), colourBands, etc
Info found only in inkjet: ink cartridges, etc
Info found only in lasers: ...
For me and many object-oriented cohorts, we prefer to quantize all the common info into one common information encapsulation, rather than define a separate struct/encapsulation for each printer type.
Then, we prefer to use a framework which would manage all the function referencing for each type of printer because not all printers print or are cleaned the same way.
So your preference/motivation oriented away from objects is telling you that your programming life is easier if you do not use objects? That you prefer to manage all those structural complexities yourself. You must not have written enough software to feel that way.
The necessity of laziness
Some people say - necessity is the mother of creativity. (as well as, Love of money is the root of evil).
But to me and my cohorts - laziness in the face of necessity are the parents of creativity. (as well as the lack of money is the other parent of evil).
Therefore, I urge you to adopt a lazy attitude towards programming so that the principle of the shortest path would kick into your life and you'll find but have no other choice than to graduate towards orienting yourself towards programming with objects.
Step 1. Read a good Design Patterns book. http://www.oodesign.com/
Step 2. Pick something you already know and rework it from an OO perspective. This is the Code Dojo approach. Take a problem that you already understand, and define the object classes.
I did this -- and wrote down what I did.
See http://homepage.mac.com/s_lott/books/oodesign.html#book-oodesign
You can do the same series of exercises to get the hang of OO design and code.
The OO mindset is based on principles that lie at a much more basic level than design patterns. Design patterns are somehow fashionable these days (and have been for a while), and they are useful, but they are just one more layer that you can put upon more basic stuff that you absolutely must learn and master if you want to do OO properly. In other words: you can do OO perfectly without design patterns. In fact, many of us did OO well before the phrase "design patterns" was even coined.
Now, there is stuff you can't do without. I suggest you start at the basics. Read and understand "Object-Oriented Software Construction" 2nd edition by Bertrand Meyer. It's probably the best book on OO programming around, both in width and depth. That is if you're interested in programming.
First, congrats on taking steps to learn something new! I hate it when developers decide to NOT evolve with technology.
As far as moving from procedural programming to OOP, I would say that one thing that you can do is take an existing app (as others have mentioned) and, before you even open a text editor, sit down and think about how each aspect of the application would be converted. I have found that more than half of OO programming is defining the conceptual objects in your mind first.
Again, I will agree with everyone's recommendations on design patterns. Specifically, I would look into the MVC (Model-View-Controller) pattern as this one might be the easiest one to grasp. You have already written code, so you should be able to look at your existing applications and begin putting each part into the M,V or C categories.
Best of luck and have fun!
There are already quite a few answers about where to find information on programming in an object-oriented fashion. Indeed, there are many great books out there that will define the basic concepts however I think the question was more on how to "stick with it" through development for someone new to the method.
Of the many concepts in object-oriented programming, the main one that will keep you on track as a newcomer is encapsulation. Does my class know how to take care of itself? Does my class have behaviour? If it doesn't, then you don't have a class, you have a structure and you'll likely be writing a lot of procedures to change its state (as it's said, "you are back to writing C in Java"). Does my class only expose methods publicly that are required for its use? Those questions may not be terribly elaborated upon but perhaps consider this thought experiment when designing your classes: What if each one of your application's classes were to be developed and maintained by a different developer on the internet and the classes also had to interact with eachother over the internet. Would each developer agree that the class they are writing and maintaining adheres to the single responsibility principle and therefore be happy that they aren't maintaining what should be someone elses code?
Regarding the design of class interfaces, consider writing all of the code that uses your classes first. Don't worry about what has to happen at the metal yet. You should be able to stub out the entire program in terms of the class relationships before you write your first bit-twiddling implementation detail. If you can't do this without twiddling bits or making a variable public, then it is time to go back to your class relationship diagram and see if you are missing an abstraction. Phrased another way, use your code before you write your code. Do this first, and you might be suprised how clean your code and interfaces turn out if you've never done it before.
While design patterns are certainly good to learn, and some are extremely powerful, they aren't generally intrinsically object-oriented and as some argue (and I tend to agree) design patterns are often just exposed weaknesses in the language. One language's design patterns is another's basic founding principles. So when starting, don't get hung up on whether or not some relationship is a good candidate for a bridge or a facade; this is not specific to object-oriented thought, this is related to what a specific language's constructs afford.
Don't.
First, learn writing. Second, learn user experience and interaction design. Third, learn business analysis. Fourth, learn role modeling.
Now that you know what objects are, you will come to see that objects are not found in code. They are found at runtime; in the space between the machine and the user's mind. This is what object orientation really means. Unfortunately recent academia has twisted it into an engineering concept. Nothing could be further off the mark. And try as they might to emulate, the end result is crap. Why? Because the "OOP" paradigm as the industry knows it today is built on a fundamentally flawed idea: decompositional analysis of identity. How is this flawed? Because identity in and of itself is meaningless. It is void. In a mathematical sense, in a philosophical sense. This is not how a human being perceives and interacts with the world.
Canon: Alan Kay, Trygve Reenskaug, James (Jim) Coplien
How I wish I was in your position. :)
I think it helps to first skim over some existing, decent, proven object-oriented code (e.g. Qt source code) so you can get a feel for "how it's done". After that, learning from a book or creating your own framework will be much more effective.
In general, it really helps to see things in context before reading about and practicing them, as it gives you moments to say to yourself, "Oh, that's why they did that!" At least that's how it works for me.
The hard part of OO is which stuff should be put together into one object. As you already mentioned the evolution of your source code, here you have a simple guideline on how to evolve your source code towards an OO design:
"Put stuff together that changes together."
When two pieces of code have similar change velocities, that's a hint that they should be placed in the same object. When the change velocities are different, consider placing them in different objects.
This is also known as "Change Velocity".
If you follow that guideline your code will naturally evolve towards a good OO design. Why?
Fragments of code often have similar
change velocities if they access a
common representation. Every time the
representation changes, all the pieces
of code that use it must change at
once. This is part of the reason we
use objects as modules to encapsulate
representation. Separating interface
from implementation makes sense under
this guideline too - the
implementation changing more often and
thus having a higher change velocity.
If a class has a stable part and an
unstable part, that's a difference in
change velocity that suggests moving
the stable part to a (possibly
abstract) base class.
Similarly, if a class has two parts
which change equally often but at
different times or in different
directions (that is to say, for
different reasons), then that again
suggests refactoring the class.
Sometimes replace "class" with
"method". For example, if one line of
a method is likely to change more
often than the rest - perhaps it is
the line which creates a new object
instance and contains the name of its
class - consider moving it to its own
routine. Then subclasses can easily
effect their change by overriding it.
I came across this concept on C2 wiki many years ago, but I've rarely seen it used since. I find it very useful. It expresses some crucial underlying motivation of object oriented design. Of course, it's therefore blindingly obvious.
These are changes of the program.
There is another sense of change
velocity - you don't want instance
variables changing at different rate,
or rather that is a sign of potential
problems. For example, in a graphics
editor you shouldn't keep the figures
and the handles in the same
collection, because the figures change
once a minute or once an hour and the
handles change once a second or once a
minute.
In a somewhat larger view, you want a
system to be able to change fast
enough to keep up with the changes in
the business.
PS: the other principle that you should follow is "Law of Demeter", that is, an object should only talk to its friends. Friends are: yourself, instance variables, parameters, locals, and members of friendly collections - but not globals and static variables.
You might consider using the CRC (Class/Responsibility/Collaboration) card approach to OO design. This is nothing too scary - just a way to sort out what your objects should be, and which object should be responsible for which tasks by writing stuff down on a bunch of file cards to help clarify your thoughts.
It was originally designed as a teaching tool for OO thought, and might work for you. The original paper is at: http://c2.com/doc/oopsla89/paper.html
A poster above suggested programming in Smalltalk to force you into OO habits, and to an extent that's a good suggestion - Smalltalk certainly did me a lot of good, but
a) you may not have the spare time to learn a new language. If you do, great.
b) I used to tutor a university course in OO programming, using Smalltalk, and the students did an excellent job of proving that old joke about how "You can write FORTRAN in any language".
Finally: when I was learning about OO (from books) I got the impression that you subclassed a lot, creating complicated class hierarchies. When I started working with OO programmers I realised it didn't happen as often as I thought. I think everyone makes this mistake when they're learning.
The only way to write better code is to write more code. Take a project you've implemented procedurally and convert it to OOP (assuming you're working in a language that supports both). You'll probably end up with a fragile, tightly coupled solution the first time around, but that's ok. Take the bad OOP implementation and start refactoring it into something better. Eventually, you'll figure out what works, and what doesn't.
When you're ready to take the next step, pick up a Design Patterns book and learn some of the OOP design terminology. This isn't strictly necessary, but it will give you a better grasp of some of the common problems and solutions.
I think you should convince yourself by researching all of the downsides with procedural programming, for example (some buzzwords following, watch out): scope, state ... practically you'd be able to extract many terms just by reading examples of design patterns (read: common examples of using objects together.)
Stressing yourself into learning something you don't believe in won't get you anywhere. Start being really critical on your earlier work and refactor it to avoid copied code and using the global scope, and you'll find yourself wanting more.
For me the ah-ha moment of OOP was the first time I looked at code and realised I could refactor common stuff into a base class. You clearly know your way around code and re-use, but you need to think around classes not procedures. With user authentication it's clear you're going to have a username and password, now they go into the base class, but what if you need a tokenId as well, re-use your existing login base class, and create a new subclass from that with the new behaviour, all your existing code works without change.
See how that works for you.
Well, first off design patterns are about the worst thing to pattern your programming to.
It's just a big set of things. It's nothing to do with OOP, and most of them such as singleton are constantly used for all the wrong reasons (ie initialization). Some of these things you have to use so telling you about them is pointless, others are counterproductive, and the rest are just special case things. If you try to learn anything this way everything will start to look like some bizarre doodad someone came up with for a very special problem or because they needed infinite genericity (which is seldom true). Don't let people con you into using a million iterators and templates for no reason and make things ten times more complicated.
Really OOP is a simple subject that gets massively overcomplicated. Unfortunately in C++ it has a lot of issues but really simple virtual methods are what matters. Pure virtual base classes used much like a java interface object are the most useful but also just plain virtual methods here and there will come in handy.
It's mostly been overblown. It also doesn't lend itself well to every problem. If you make database and gui stuff it lends itself well to that. If you make system tools it is usually not as helpful.
I found that one of the things which has really helped solidify the benefits of OOP for me has been writing unit tests with a mock object framework (such as EasyMock). Once you start to develop that way, you can see how classes help you isolate modules behind interfaces and also allow for easier testing.
One thing to keep in mind is that when people are first learning OOP, often there is an overemphasis on inheritance. Inheritance has its place, but it's a tool that can easily be overused. Composition or simple interface implementation are often better ways of doing things. Don't go so far in attempting to reuse code via inheritance that you make inheritance trees which make little sense from a polymorphism standpoint. The substitution principle is what makes inheritance/interface implementation powerful, not the fact that you can reuse code by subclassing.
A great step would be to start of with a OOP framework, you can still write procedural code in the framework but over time you can refine your coding habits & start converting functionality into objects.
Also reading about patterns & data modeling will give you more ideas about to code your logic in a OOP style.
I have found that a very intense way learning to train abstraction in programming is to build a OOP library with a defined functionality, and then to implement two projects with similar but still different requirements that are building on that library, at the same time.
This is very time-consuming and you need to have learned the basics of OOP first (S.Lott has some great links in the other answer). Constant refactoring and lots of "Doh!" moments are the rule; but I found this a great way to learn modular programming because everything I did was immediately noticeable in the implementation of one of the projects.
Simply practice. If you've read everything about OOP and you know something about OOP and you know the OOP principals implemented in your language PHP... then just practice, practice and practice some more.
Now, don't go viewing OOP as the hammer and everything else as the nail, but do try to incorporate at least one class in a project. Then see if you can reuse it in another project etc..
Learn a new language, one that helps to move you gently to OOP. Java is nice, but a bit bloated, though. But its system library is mainly OO, so you are force to use objects.
Moving to another language also helps you not to reuse your old code :-)
I think it´s important to learn the theory first. So reading a book would be a good start.
I believe that the mechanics of OOP seem completely arbitrary and make no sense until you read a book on design patterns and understand the "why" of it. I recommend Head First Design Patterns. I thought OOP was ridiculous and completely useless until I picked up this book and saw what it was actually good for.
OO makes a lot more sense when you understand function pointers and how it relates to indirect function calls and late binding. Play around with function pointers in C, C++, or D for a little while and get a feel for what they're for and how they work. The polymorphism/virtual function part of OO is just another layer of abstraction on top of this.
Procedural is the right tool for some jobs. Don't act like it's wrong. IMHO all three major paradigms (procedural, OO, functional) are valuable even at a fine-grained level, within a single module. I tend to prefer:
Procedural is good when my problem is simple (or I've already factored it enough with functional and OO that I now have a subproblem that I consider simple) and I want the most straightforward solution without a lot of abstraction getting in the way.
Object-oriented is good when my problem is more complex and has lots of state that makes sense in the context of the problem domain. In these cases the existence of state is not an implementation detail, but the exact representation is one that I prefer to abstract away.
Functional is good when my problem is complex but has no state that makes sense at the level of the problem domain. From the perspective of the problem domain, the existence of state is an implementation detail.
As far as I know, and have gathered from other SO posts, there are no proper tools for refactoring PHP code yet, so when it comes to refactoring, it's probably good old search-and-replace for most of us, with a good amount of praying that we didn't overlook something.
I would like to know whether there are any coding recommendations on how to write code friendly for manual refactoring. Never to construct variable names from strings, would be one thing that comes to mind because a construct like that is impossible to grep:
$object->{"field_".$fieldname}
I could imagine there are several such do's and don'ts. Maybe somebody knows good resources / articles on the issue. It wouldn't have to be PHP specific, either.
Unit tests always help me identify places where I've broken code due to a refactor. Unit tests in dynamic languages (PHP, Ruby, Python, etc.) provide assistance where static typing in other languages (Java, C#) would typically allow you to more safely refactor.
Avoid magic as much as possible: variable variables, eval, masking errors with # and storing code in the database will come back to bite you.
Well, The best way to write refactoring friendly code is to write loose coupled ,highly cohesive code and object oriented code.
You should try as much abstraction as you can, after all abstraction is the keyword while programming.
Moroever, you should be layering your code into presentation layer, business layer, data layer etc.. and Using design patterns is a pretty good solution.
I d recommend you to read Martin Fowler.
Your question makes a certain amount of sense. But—at the same time—it implies that the implementation is known to be inadequate, and written to be replaced. Why not just architect it properly the first time?
First, make sure your variable names make sense. If possible, go as OOP as you possibly can, or at least keep everything organized (image function file, database file, etc)
Second, and this is handy, check your IDE. Netbeans has options for refactoring. You can search in a file, in a folder, in a project, etc.