How to Do Prototype Based Programming with Io
Learn to program using Io - OOP with prototypes
Nov 10, 2008
One of the interesting things about using classes in a programming language such as Io is that it doesn't actually use classes. Instead Io uses a concept known as prototyping, which makes Io a very easy programming language to understand.
A new user can be up and running in just a matter of minutes - even if they've never written any code before.
The Concept of Prototyping
The core to prototyping is cloning - a prototype object is created and then this is cloned to produce new objects. This concept can easily be demonstrated by looking at Io.
Downloading Io
Both Windows and Linux can be obtained from the Io download page at http://www.iolanguage.com/downloads, and the installation is simple:
- Windows - download the binaries zip file to the C: drive, and then uncompress it - the result will be a directory named C:\usr\local\bin and it's here that the Io program lives
- Linux - download the tarballs, uncompress and run:make vmsudo make install
On some versions of Linux a little extra work may be needed
Running Io
Io can by run in any of three ways:
- calling Io directly from the command line, for example:$ ioIo> writeln ("Hello World")
- using Io to load a script file:io <my Io script file>
- make an Io script file executable and then run that from the command line
An Io Script: Prototypes and Clones
The first line of any Io script should be the shebang line; this tells the system that the Io interpreter is to be used:
The key thing that this script will do is to create a prototype (in this case a car), and it's interesting to note that the car (at this stage) is just a clone of Io's default object:
At the moment car is just an blank object, however it is very easy to add properties and methods to the basic object:
To make another object the programmer can clone the original and then make use of it:
If the script were to be run now then the output would be:
Expanding the Prototype
In this example a simple prototype (the car) was created and cloned (the jeep), however it is still possible to add further properties and methods to the prototype:
and these additions will passed on to any clones automatically:
with an output of:
And, of course, further clones can be created:
Conclusion
Io provides an excellent introduction into prototype-based programming and provides the programmer with:
- the ability to create a prototype
- the ability to create clones from the prototype
- behaviour reuse -allowing the clone to automatically pick up properties and methods from the prototype
It is all so simple that even a complete novice can program with Io with complete ease.
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