I just wanted to quickly go over the differences between these, because I’d been confused when I first learned them.
Classes in ruby are defined by
class Person end
Now, when we create an instance of person…
new_person = Person.new
attr_writer
…we might want to give this new person a name.
new_person = Person.new new_person.name = "Hyung Cho"
However, because we don’t have a writer method to our class, this will give us the following error `<main>': undefined method `name=' for #<Person:0x0000000101ab20> (NoMethodError)
We can create a writer method in two different ways in Ruby. The first is to use attr_writer:
class Person attr_writer :name end
Because writer and reader methods are so commonly used, Ruby has a built in ‘magic’ function that creates them. To write multiple writers or readers, we can separate them with commas.
The second is to define it this way:
class Person
def name=(name)
@name = name
end
end
These methods are identical, and taking a closer look at the second method might give us a better understanding of what our writer method is actually doing. We’re creating a method name= that takes one argument name and setting it to our instance variable @name. So now, when we try setting our name variable to our name, it doesn’t give us an error.
class Person attr_writer :name end new_person = Person.new new_person.name = "Hyung Cho"
Remember, new_person.name = "Hyung Cho" is the same thing as new_person.name=("Hyung Cho"). If you take a look at it you’ll see that we’re just calling the name= method!
attr_reader
Now, let’s say that we want to find out the name of our new_person. The obvious way is to try puts new_person.name. However, that won’t work.
When you throw Ruby puts new_person.name, what you’re telling it is to print whatever the method name returns. At this point however, we don’t have the method name defined. This is called a reader method. Whereas the first writer method has us assigning an instance variable through a writer method, our reader method has us calling another method so we can read that instance variable. Once again, we can accomplish this in two ways:
class Person attr_writer :name attr_reader :name end
and the other way,
class Person
def name=(name)
@name = name
end
def name
@name
end
end
So now,
class Person attr_writer :name attr_reader :name end new_person = Person.new new_person.name = "Hyung Cho" puts new_person.name
will return
>> Hyung Cho
attr_accessor
With both the reader and writer methods understood, we can combine them into a simpler attr_accessor which creates both.
class Person attr_reader :name attr_writer :name end
is the same thing as
class Person attr_accessor :name end
Simple, right?!
Initialize
The initialize method is different than the writer and reader methods even though it may seem similar. Think of initialize methods like this: when you call a method that takes in an argument, let’s say for example
def add_two_numbers(num1, num2) num1 + num2 end puts add_two_numbers(1, 2) >> 3
num1 and num2 get initialized locally. Similarly, setting initialized variables just tells ruby that when an instance of this class gets created, some specific variables will be created. Here’s an example:
class Person
attr_reader :name
def initialize(name)
@name = name
end
end
new_person = Person.new("Hyung Cho")
puts new_person.name
>> Hyung Cho
If you now try to create an instance of the Person class without throwing it an argument like so
class Person
def initialize(name)
@name = name
end
end
new_person = Person.new
it will give you an error `initialize': wrong number of arguments (0 for 1) (ArgumentError)
Don’t be mistaken, an initialized variable does not always need to be thrown as an argument when the object is created. Your initialize method can look something like this:
class Person
def initialize(name)
@name = name
@school = "Crescenta Valley High School"
end
end
We will never pass in a school argument in the creation of a Person object, but the moment an instance of Person is created, it will automatically set the instance variable @school to "Crescenta Valley High School
There you have it! First time blogging about a technical subject, so any feedback would be appreciated! I tried to explain it in the simplest way possible for beginners to understand.
Coder.lyfe 