Ruby - More Classes and Objects

Ruby module R108

More Classes and Objects

Exercises, examples and other material relating to training module R108. This topic is presented on public courses Learning to program in Ruby, Ruby Programming

Background

Beyond the basic classes, you'll wish to use the power of interitance, encapsulation and polymorphism. Don't worry if these are new terms to you - they're explained in this course module.

Related technical and longer articles

Modules, Mixins and Comparators in Ruby
Basic class definition and use in Ruby

Articles and tips on this subject		updated
4551	Testing your new class - first steps with cucumber A recent article ([here]) showed you how we build up a series of classes, each with their own piece of test code, into applications. It's all very well putting a piece of test code in the bottom of our class definition file - and that's a useful thing to do - but it's just a single test, and it doesn't ...	2015-10-23
4550	Build up classes into applications sharing data types in Ruby I've put together a "build-up" example showing code shared between multiple applications and using multiple classes in Ruby. Start with stations.rb which defines a railway station object and includes a factory to load a Hash of all UK stations. There's also a test program in there so that it can run ...	2015-10-23
4504	Where does Ruby load modules from, and how to load from current directory All (scripting) languages allow you to load code from other supporting source files, using keywords like use, load, source and include. In Ruby, the most common way to load other code is to require it - and if you use the require method you'll load in code from another file which will be assumed to ...	2015-06-03
4366	Changing what operators do on objects - a comparison across different programming languages In Object Oriented languages, you used named pieces of code known as methods to perform an operation on a variable - for example you might write weeklist.extend(weekend) to take a list of (something) for a week and add a list relating to weekend onto the end of it. Sometimes, the method ...	2014-12-30 (longer)
2980	Ruby - examples of regular expressions, inheritance and polymorphism With delegates on public Well House Consultants courses staying in our on-site accommodation, there's time for them to learn a lot more about each other's applications and get a far wider view of the uses of the subject they're with us to learn. There's time for the delegate who wants to extend practicals ...	2013-01-01
3782	Standard methods available on all objects in Ruby There are a lot of things I can do with any object in Ruby - there's a whole package deal of methods available to me by just defining and creating an object: irb(main):003:0> class Thing irb(main):004:1> end => nil irb(main):005:0> widget = Thing.new => #<Thing:0x98c1e74> irb(main):006:0> widget.methods => ...	2012-06-30
3781	Private, Protected, Public in Ruby. What about interfaces and abstract classes in Ruby? There's no requirement for you to use the words "public", "private" and "protected" in Ruby - methods within classes that you write default to being public anyway. But you may wish to protect certain of your methods from being called directly by the users of your classes. So - what protection do they ...	2012-06-30
3760	Why you should use objects even for short data manipulation programs in Ruby It's so easy to take the "Bull at a gate" approach - to start writing code to do the job in hand without giving thought to code-reuse later on, or indeed to how the work can be used again later. And it's double easy to, for me to take the bull approach during a course, where I'm writing a short demonstration ...	2012-06-16
3260	Ruby - a training example that puts many language elements together to demonstrate the whole Towards the end of our programming language training courses, we pull together all the various strands into a worked example that shows how they go together. I've just posted such an example from last week's Ruby Programming Course ... [here]. Let's have a look at some of the things in the example ...	2011-04-23
3158	Ruby training - some fresh examples for string handling applications Ruby's a great language. No - let me rephrase that "Ruby's a fantastic language" ... for many tasks such as "data munging" - handling / manipulating large flows of data, in all sorts of ways. But in my training role, I come across far more people using Ruby on Rails, Selenium and Watir than Ruby for ...	2011-02-10
3154	Changing a class later on - Ruby In Ruby, you can define a class ... and then come back and add methods to it. But why would you want to? Let's suppose that you've got a base class - I'll use "Rectangle" as my example, and you've already subclassed it to "Square" and perhaps a few other things, via a required file that you share between ...	2011-02-02
3142	Private and Public - and things between A public train service is one which is available for anyone to travel on; a private one only takes limited passengers as invites / made available by the operator. And there could be intermediate levels too - I understand that at times the British Transport Police protect the last train from Weymouth ...	2011-01-25 (longer)
2977	What is a factory method and why use one? - Example in Ruby How do you create an object? By calling a constructor method, of course. But ... actually ... there's no "of course" about it. Here's a piece of code from an example I wrote yesterday: sageroll.push Transact::factory(current) and that call creates an object ... Whilst you can create ...	2010-09-30
2717	The Multiple Inheritance Conundrum, interfaces and mixins Should an OO programming language support "multiple inheritance"? Let's define multiple inheritance first - starting from simple (single?) inheritance. (Single) Inheritance. I don't want to have to define each type of thing ("class of object") from scratch, so I'll define once class as being based ...	2010-04-13
2620	Direct access to object variable (attributes) in Ruby Rather than writing getters and setters, in many Object Oriented languages you can access the variables within an object directly. That can be dangerous for code flexibility for the future, as it means that you're removing the possibility of interspersing code. However, it can be very convenient. In ...	2010-02-02
2616	Defining a static method - Java, Python and Ruby Most methods in classes that your write will be run on / applied to individual objects within that class - you'll be asking for the colour of a marker pen, or setting the price of a hotel room. You will NOT - typically - have a model in which all marker pens share the same colour. But - just occasionally ...	2010-02-01
2604	Tips for writing a test program (Ruby / Python / Java) Where does my test code go? If you've written a class - a series of methods to be used within another application - how do you test it? How about writing a test program within the same file which runs as the main program if you run your class on its own from the command line, but is ignored if you ...	2010-01-30
2603	Ruby objects - a primer If you're new to Ruby, but familiar with Object Oriented Programming, you might like to take a quick look at the example that I wrote during yesterday's course which shows how all the major OO elements are implemented in Ruby. The sample source is [here]. Here are some of the key facts: • Classes ...	2010-01-29 (longer)
2601	Ruby - is_a? v instance_of? - what is the difference? In Ruby, have you ever wanted to know if an object is of a particular type? The instance_of? method will return a true value if an object is of the type given as a parameter. However, instance_of? will return a false if we use it to check whether an object inherits from another class. So it's an ...	2010-01-28
2292	Object Orientation in Ruby - intermediate examples It's when you teach object orientation - the fully Monty, including inheritance, static and dynamic methods and variables, and so on - to a complete novice to programming and that person finds it's one of the easiest parts of the course that you realise: a) Just how many bad ole habits us ancient structure ...	2009-07-17
1587	Some Ruby programming examples from our course I was giving a Public Ruby Course to a small group at the end of last week ... and having a small group gave me the opportunity to write some demonstrations in front of them. I have now tidied these up and have pleasure in presenting to more Ruby demonstrations: Ruby's BEGIN block The compact method ...	2008-03-21
1217	What are factory and singleton classes? Do you find some of the OO terminolgy baffling? Once you've learnt about constructors and methods, inheritance, overloading and polymorphism and statics, you might think you're there. Then someone mentions a "factory class" or a "singleton" ... Fear not - factory and singleton classes are posh names ...	2007-06-08
184	MTBF of coffee machines Updated - see end of story REAL coffee. Mmmmmm. Ever since we started running courses here, we've provided customers with superb coffee. Grind the beans as required, brew the coffee with freshly heated pure water and supply a choice of sugars and sweeteners for those who want such things. Our first ...	2006-12-03
656	Think about your design even if you don't use full UML Even if you don't feel that your project is big enough to get involved with formal design methods, many of the lessons of UML and some informal design diagrams can help you get a clear view of what you're going to be doing be for you start, and can help you come up a good, thought out and reliable plan ...	2006-06-05

Examples from our training material

O1.rb	Amending a base class even after it has been extended
O2.rb	Copy v clone
attr	attribute accessors
cmquick	static and dynamic member variables and methods
d4_2	Single class example for extension by inheritance
d4_3	Object and Class variables (dynamic and static)
d4_4	Static Method
d4_5	Inheritance in Ruby
disc2	Comparator methods (larger and smaller)
dub2	With $ - variables are global
dub3	no returns on a Ruby method
dubber	default - variables are LOCAL
finex	Simplest Inheritance Example
food.rb	Single class demo
in4.rb	Inheritance, factories, statics, DATA, lazy ops, to_s
inh1.rb	Inheritance in Ruby
journey.rb	Sample class used in sharing example
multifood.rb	Class demo - lots of extras
ob2.rb	A class with some class (static) and singleton members
olop.rb	Operator overloading
overload_add.rb	Operator (+) and to_string overloading, Ruby
reallyshort	Inheritance, Class methods, Attribute Accessors, operator overloading
second	second program that uses classes
slash	Server Log Analysis (2)
slogan	Server Log Analysis
stanley	Listing of standard methods
station.feature	gherkin / features of station class
station_steps.rb	Cucumber implemented test code for station.feature behaviour
stations.rb	Sample class used in sharing example
stobsort	Data manipulation - object approach
ststsort	Data manipulation - structured approach
third	third example use of classes
transact.data	Class / Interitance / Test program data
transact.rb	Class / Interitance / Test program example showing good practise
transport.rb	Cluster of related (inheriting) transport classes and test program

Background information

Some modules are available for download as a sample of our material or under an Open Training Notes License for free download from [here].

Topics covered in this module

Public, private and protected visibility.
Singletons and defs.
Inheritance mixins, and super.
Destructors and garbage collection.
Namespaces and modules.
Hooks.
Freezing objects.
Calling methods with code blocks.
Looking inside objects - reflection.

Complete learning

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