User Defined Function Libraries Vs. Includes

travelbuff

I would like to discuss the performance impact and benefits of using user defined functions in our scripts. There are sometimes when the benefit of writing a function is obvious to me, such as doing date formats in and out of mysql format - saves a hell of a lot of repetitive coding.

However, I tend to think that sometimes a function just slows things down. For example, I see a lot of scripts that us a dbconnect() function that is stored in a included function library. To me, you are better off just writing the code normally and saving it as a file then calling it as an include. Either way, you have to have an include, and if you do it as a function you then have to call the function.

Another drawback I see to user defined functions is that if you store them in a function library and include the libray in each page, doesn't the parser have to read the whole library every time the page loads whether you call one function or ten? I use one classifieds script that includes a function lib of about 30 functions on every page though most pages only use 3 or 4 at a time.

Anywhoo, I would be interested in hearing others thoughts on when to create functions and libraries and when to just call separate code snippets for repetitive tasks.

ShadowMetis

The way I see it, the only reason for user defined functions is something very big. If you're doing a whole class or something you definately need to do it once and include it in the rest. Besides that you shouldn't be so lazy and just type it out.

laserlight

For example, I see a lot of scripts that us a dbconnect() function that is stored in a included function library. To me, you are better off just writing the code normally and saving it as a file then calling it as an include. Either way, you have to have an include, and if you do it as a function you then have to call the function.

In this case, you're looking at what is called a database abstraction layer.
Now, coding this way definitely is slowly than say, using mysql_* functions right away for a mysql database.
But what happens if you decide to use a postgresql database instead?
With a database abstraction layer, you will not have to drastically modify your main code to account for this.
PHP Builder's Best Practices: Database Abstraction article might be a good read here.

Another drawback I see to user defined functions is that if you store them in a function library and include the libray in each page, doesn't the parser have to read the whole library every time the page loads whether you call one function or ten?

From what I understand, PHP4 makes more than one pass on the PHP script.
This is why a function can be defined after it is used in a script.
So yes, all the functions would be read, at least on the first pass.

I'm not too sure if opening 2 include files and parsing them will be as expensive as opening 1 include file with the same code and parsing them.
I suspect that there is a cost to opening an include file.
If this is true, then if you have to call 20 functions, and so have to include 20 files, there may be a cost to that in opening the include files that may outweigh not having to read extra code that isnt actually run, merely read.

ShadowMetis

Postgresql is sort of a different case though. It's not the same as the simple mysql_connect. Not as popular also, I believe.

travelbuff

Shadow:

The way I see it, the only reason for user defined functions is something very big.

I dunno - if you consider the date formatting I mentioned, it is really helpful. I have a bunch of scripts that use forms that have a date field generated from a pop up calendar, and I want the user to see the date in regular format, so I have to reformat that set of dates (3 per script) date all of the time. I wrote a function that is called in an include that reformats the dates for me. VERY helpful, and a perfect example of an ideal application for a user defined function IMHO.

Laserlight:

Originally posted by laserlight
With a database abstraction layer, you will not have to drastically modify your main code to account for this.
PHP Builder's Best Practices: Database Abstraction article might be a good read here.

Good article, thanks! I really need to learn more about object oriented coding as discussed on p2.
I do use an abstraction layer for the db connection and info, but rather than doing it inside a function I just keep the code in a separate file and include it.

From what I understand, PHP4 makes more than one pass on the PHP script. This is why a function can be defined after it is used in a script.

Wow, I didn't realize that you could call a function before you defined it. I guess I need to spend more time on the manual 🙂

I suspect that there is a cost to opening an include file.
If this is true, then if you have to call 20 functions, and so have to include 20 files, there may be a cost to that in opening the include files that may outweigh not having to read extra code that isnt actually run, merely read.

You make an excellent point. Maybe the way to do it is to use small collections of code snippets that are often used together - for example, I could have one include that used common code required for handling forms, another that had common code for retrieving and displaying data, etc. The classifieds script I mentioned (phpclassifieds from Delta Scripts) drives me nuts because there are so many lines of unused code included on every page and it really makes it seem bloated, and has to cost overhead.

superwormy

Aight, firstly, I highly doubt that you'll ever notice a performance decrease between a script without functions and a script with functions. The difference between with and without is probably on the order of like 0.001 seconds, which is extradinarily negligable.

Secondly, functions make projects of any substantial size WAYYYY more manageable and maintaiinable. Anyone who doesn't realize this hasn't done enough programming yet.

Thirdly, dividing programs/scripts/projects into functions enables more than one developer to easily work on one project without interfering with each other. One guy can write some functions, and everyone else can use them.

Copy/Paste programming is BAD. It leads to messy code and bug ridden programs. If you need to continuously retype sections of code or copy/paste them, YOU SHOULD BE USING FUNCTIONS TO TAKE THE PLACE OF THAT CODE INSTEAD!

Sometime read about Model/View/Controller theory too, it absolutely requires the use of objects/functions, and has great benefits for larger projects.

laserlight

I do use an abstraction layer for the db connection and info, but rather than doing it inside a function I just keep the code in a separate file and include it.

Generally it is advisable for a file containing the username/password to be kept outside the document root, if possible, so that the file cant easily be compromised if say, PHP happens to fail to parse it.

I must confess that I didnt really read you well :o
I thought that you were just comparing using include files for each function, rather than substituting functions with include files.

As superwormy mentioned, in most high level programming languages this is bad practice.
There may be problems in "hidden" variables, e.g. a namespace collision.
Also, your efficiency may actually be reduced instead, since it is possible that the parser has to read the code twice, rather than read it once and then execute it twice, if you're using that particular block of code twice.
I dont hack PHP though, so I cant really say for sure.

I dont think anyone can fault you on the dbconnect() case though, since the code should be run only once per script, and shouldnt involve many variables.
The part where a DB abstraction layer becomes useful is in actually handling the queries.