PHP

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.

Since my last visit to this subject I have been thinking about how to represent a collection of random colors so that it looks sorted and that no information is lost during that process. I quickly realised that I needed to use all three aspects of the color space, which lends itself to generating 3D objects. Indeed, the red, green, blue color space is built around a cube so it can often be represented as a cube.

The hue, saturation, and value color space is built around the concept of a cylinder, which means that 2 of the axis lend themselves to a circumference of a circle (the hue) and the diameter of a circle (the saturation). This is an example of the polar coordinate system. We can therefore draw a circle using hue and saturation and the value can be used to represent a different aspect of the color space.

Since my last post, where I talked about drawling a line with pixels in PHP, I have been looking at drawing circles. As it turns out, there are a few different ways to draw a circle, so I'll go through a few options here.

To start with, there are some built in functions in PHP that can be used to draw an arc, circle or ellipse as a filled in shape or a line. The built in function in PHP called imageellipse() that can be used to draw a circle. This is part of the GD library.

Whilst working on a project recently I hit upon a PHP error that I've never seen before. During a process where a soap service was calling an API the connection would fail and the program would fatal error and stop.

I had protection mechanisms in place to catch this kind of connection error, but the fatal error was caused when the program tried to throw the exception I had put in place to indicate a failed connection.

Here is the error message (with some of the detail removed). This is a Drupal site but that detail is irrelevant to the problem.