Introducing the concept of a class
First and foremost, classes help a programmer to organize his or her code. On a more abstract level, classes are one of the defining features of object oriented programming, so I find it easier to explain what a class is by explaining its relationship to Object Oriented Programming in general.
Finding classes of objects in real life
In the real world, almost everything around us can be thought of as an object. A chair is an object, a laptop is an object, a dog is an object. Thinking in these terms can make it easier to understand the world: An animal is an object. A dog is an object. A cat is an object. And these three objects are related in the sense that cats and dogs are animals. That type of relationship is helpful for us to consider when thinking about dogs and cats.
It also helps a person to program a big and complicated program if different parts of the program can be broken up into different "objects", and those objects can have clearly defined relationships. This brings us to the main point of this article: Classes. Classes are used to clearly define those relationships between different parts of a code.
Before this class concept is applied to the creation of a helpful program, many programming books and tutorials first apply the concept to silly examples from the real world. I will follow suit. Here I am going to create a Rapper class.
Our silly rapper class
In the real world, some might see a "rapper" as a relatively broad category,
and there may be more specific kinds of rappers within that class such as
"gangster rapper", "commercial rapper", "underground rapper", etc. But, before
we get into those specifics, the first step is to create a rapper class like so:
class Rapper
end
However, before a class can be used throughout a program, it must be "initialized".
It's kind of like how a rapper, before his sick flows can be shared with the
rest of the world, he must be signed to a record deal. The initialize method
looks like this:
def initialize(real_name)
if real_name == signed_to_major_label
@rapper = stage_name
else
broke_artist = real_name
end
end
That code can be used to create a new instance variable which is simply an example
of that class. Then, the instance variable can be used throughout the program. Or,
getting back to our corny analogy, the rapper is free to tour across the nation.
In this example, I also threw in a real_name argument variable that
can accept a sring of the rappers real name, and then it can test whether that
rapper has been signed to a major label.
A class within a program may also include methods that can be used throughout that program.
Getting back to our analogy:
def spit_rhymes(words)
return rand(words) + "by #{rapper}"
end
def make_beats(record_samples)
return rand(record_samples) + "produced by #{rapper}"
end
def featured_on_slow_song(singer, song)
remix = song.map(verse) do |verse|
verse << spit_rhymes
end
return remix + "featuring #{@rapper}"
end
In the code above, three methods were created that each could be used inside of the Rapper class.
Typical of Ruby class methods, each of those methods includes an instance variable drawn from the
initialize method. Data can be created when one runs the initialize method:
drake = Rapper.new("Aubrey Graham")
meek_mill = Rapper.new("Robert Williams")
You may notice that when the two lines above call the initialize method, the result is stored in a variable.
That way, the class methods can be called on that variable, and the program will understand
that it needs to use the instance variable that was created when the intialize method was first run. Code like this:
drake.featured_on_slow_song("Joanna Newsom", "Sapokanikan")
Hopefully the use of a class is not lost on the analogy. But, classes are all about these dynamic relationships between objects, methods, and the data that passes between them.