Table of Contents
What is a getter method?
A getter method is a method that gets a value of an instance variable. Without a getter method, you can not retrieve a value of an instance variable outside the class the instance variable is instantiated from.
Here is an example.
class Movie
def initialize(name)
@name = name
end
end
obj1 = Movie.new('Forrest Gump')
p obj1.name #=> undefined method `name' for #<Movie:0x007fecd08cb288 @name="Forrest Gump"> (NoMethodError)As you can see, the value of obj1 (name) can not be retrieved outside Movie class. if you try to retrive a value of an instance variable outside its class without a getter method, Ruby raises No Mothod Error.
Now, Let’s see how to retrieve the value of obj1 outside Movie class with a getter method.
All you have to do here is to define a getter method named name. Though the name of a getter method can be anything, it is common practice to name a getter method the instance variable’s name.
class Movie
def initialize(name)
@name = name
end
def name
@name
end
end
obj1 = Movie.new('Forrest Gump')
p obj1.name #=> "Forrest Gump"What is a setter method?
A setter is a method that sets a value of an instance variable. Without a setter method, you can not assign a value to an instance variable outside its class. if you try to set a value of an instance variable outside its class, Ruby raises No Method Error just like it does when you try to retrieve a value of an instance variable outside its class without a getter method.
class Movie
def initialize(name)
@name = name
end
def name #getter method
@name
end
end
obj1 = Movie.new('Forrest Gump')
p obj1.name #=> "Forrest Gump"
obj1.name = 'Fight Club' #=> undefined method `name=' for #<Movie:0x007f9937053368 @name="Forrest Gump"> (NoMethodError)Defining a setter method inside a class makes it possible to set a value of an instance variable outside the class. You can define a setter method like the code below.
class Movie
def initialize(name)
@name = name
end
def name #getter method
@name
end
def name=(name) #setter method
@name = name
end
end
obj1 = Movie.new('Forrest Gump')
p obj1.name #=> "Forrest Gump"
obj1.name = 'Fight Club'
p obj1.name #=> "Fight Club"By using name=, you can now assign a new value Fight Club to obj1.
What are accessors?
Accessors are a way to create getter and setter methods without explicitly defining them in a class.
There are three types fo accessors in Ruby.
attr_readerautomatically generates a getter method for each given attribute.attr_writerautomatically generates a setter method for each given attribute.attr_accessorautomatically generates a getter and setter method for each given attribute.
First, let’s take a look at attr_reader!
As you can see in the code below, name and year are retrieved outside Movie class even though there is no getter method for either of them. This is because attr_reader generates a getter method for each given attribute.
class Movie
attr_reader :name, :year
def initialize(name, year)
@name = name
@year = year
end
end
obj1 = Movie.new('Forrest Gump', 1994)
p obj1.name #=> Forrest Gump
p obj1.year #=> 1994Second, let’s see how attr_writer works!
As I mentioned above, attr_witer generates a setter method for each given attribute. Therefore you can assign new values to ob1 without explicitly writing setter methods for name and year!
class Movie
attr_reader :name, :year
attr_writer :name, :year
def initialize(name, year)
@name = name
@year = year
end
end
obj1 = Movie.new('Forrest Gump', 1994)
obj1.name = 'Fight Club'
obj1.year = 1999
p obj1.name #=> "Fight Club"
p obj1.year #=> 1999Last but certainly not least, attr_accessor does what attr_reader and attr_writer do with just one line of code! It will automatically generate a getter and setter mehod for each given attribute.
class Movie
attr_accessor :name, :year
def initialize(name, year)
@name = name
@year = year
end
end
obj1 = Movie.new('Forrest Gump', 1994)
obj1.name = 'Fight Club'
obj1.year = 1999
p obj1.name #=> "Fight Club"
p obj1.year #=> 1999