PHP

I was looking at some malfunctioning code the other day where the price was pulled out of one API service and sent to another API. The problem stemmed from the fact that the value coming out of the first API was as a string and the second API required the price in pence as an integer.

The difference in formats here meant that the number had to be converted from one format to another. During this process it was found that the value was sometimes out by a single pence.

For example, whilst the first API sent over a value of £20.40, the second API received a value of 2039, which is one penny out. This class did have some unit tests, but the tests but had failed to account for this rounding error.

As it turned out, this wasn't the only problem with the class in question, so I thought I would write up a quick PHP:CSI showing the problems and how I solved them.

The other day I was tasked with creating the weekly quiz for my family. I decided it would be good to do a section that would consist of 10 words that were spelled using symbols of the chemical elements. The questions would be presented as a list of element names, like this.

Barium Carbon Potassium Tungsten Argon Darmstadtium

This breaks down to the element symbols in the following way.

Barium = Ba
Carbon = C
Potassium = K
Tungsten = W
Argon = Ar
Darmstadtium = Ds

Putting that all together we spell out a word.

BaCKWArDs

Backwards!

After a bit of thinking about what words I could use I decided to write a program that would help me. The questions in the quiz did not go down very well, but I thought I would put the code that I used here.

The first thing I did was to set up an array of elements that I could use to compare parts of words with.

Deployer is a PHP based deployment tool that I have been using very successfully for a number of months now. It comes with a number of different recipes to deploy a variety of PHP based applications, including Laravel, Symfony, Yii, and Drupal.

I first found Deployer when looking for a deployment package that suited my needs. Phing had been my tool of choice for a number of years, but it had proved problematic trying to debug the XML syntax when things needed tweaking. As I was deploying PHP applications it made sense to me to use a PHP based system to do the deployment. I looked at tools like Capistrano, but as I wasn't that familiar with Ruby I was worried that I wouldn't be able to debug mistakes or customise the deployment process easily.

The other day I was trying to print some output to the command line and then overwrite the output afterwards. It turns out that there are a couple of ways to do this so I thought I would detail a few of them here.

By far the simplest way of doing this is to run the "clear" command, which we can run via the system() function in PHP. This will clear the output of the command line ready for you to print out whatever you need. The downside to this is that the entire terminal window is cleared. Another downside is that once the output is complete scrolling up will reveal the output that was cleared out.

I was saddened to hear of the passing of the Mathematician John Horton Conway today so I decided to put together a post on his 'game of life' simulator.

This game of life, more commonly called Conway's game of life, was devised by John Conway in 1970 and is a way of modelling very simple cell population dynamics. The game takes place on a two dimensional board containing a grid of orthogonal cells. The game is technically a zero player game in that the initial setup of the game dictates the eventual evolution of the board.

The rules of the game (taken from wikipedia) are as follows.

One technique I find useful, especially when drawing images, is to invert a number on a scale. In PHP, coordinates in an image are drawn from the top left of the image. This means that if we want to draw from the bottom left then we need to invert the y coordinate.

The following is example PHP code that creates an image with a single, diagonal line, drawn across the middle.

The other day I was conducting a code review and found that a developer had used a trait to give two classes the same group of utility methods. Whilst there was nothing wrong with this in terms of functionality, I asked the developer why they had chosen to use traits instead of inheritance. We eventually decided that an inheritance model would be better suited to the situation but I thought I would go through some of the thought processes here.

What Is A Trait?

A trait, if you weren't aware, is like a class, but you don't instantiate it directly. Traits are defined using the trait keyword and are otherwise quite like a class in structure.

The idea is that code is essentially copied into the class you want to use it in from the trait and the class acts like it had that code all along. For example, let's take a simple trait.

Stream filters allow changes to be made to textual data in streams. This allows text to be changed when writing to or reading from streams, instead of changing the text after the stream has been run. There is a framework built into PHP that allows custom filters to be added to the group of built in filters.

Part of the strength of PHP's stream wrappers is the ability to add our own stream wrappers to the list of available wrappers. We can therefore natively open any type of resource just by registering a stream wrapper and then using the normal fopen() functions. The custom stream wrapper functionality is made possible through a few functions built into PHP.

Streams are a way of generalising file, network, compression resources and a few other things in a way that allows them to share a common set of features. I stream is a resource object that has streamable behaviour. It can be read or written to in a linear fashion, but not necessarily from the beginning of the stream.

Streams have been available in PHP for quite a while (at least since version 4.3.0) and are used pretty transparently by most PHP programmers. They can be used to access files, network resources, command line arguments, pretty much anything that goes through the input/output stream in PHP.

I was recently looking at ReactPHP and found that the use of streams was a requirement in order to prevent blocking the input/output stream. Although, I had seen streams being used in PHP applications, I wasn't entirely certain how to use them myself. As a result I thought I'd put together a post about them.