Ruby Monstas

Attribute Writers

What we know so far

For now, we could only input data into an object when initializing it.

Person class

class Person

  def initialize(name)
    @name = name
  end

  def name
    @name
  end

end

person = Person.new("Jenny")
          
person.name
# => "Jenny"

We can: set the name in the constructor, get the name via name method (reader)

How would you set a value?

We know how to set a variable value:

name = "Mary"

So how could we set a new name on an object?

person.name = "Mary"

Let's look at our Person example again:

class Person    
  def initialize(name)
    @name = name
  end

  def name
    @name
  end
end

and add a writer:

class Person          
  def initialize(name)
    @name = name
  end

  def name
    @name
  end

  def name=(new_name)
    @name = new_name
  end
end

We add a new method that ends with the "=" sign.

This is the magic so it can be used like a variable assignment.

Technically we would have to call the writer like this:

person.name=("Mary")

but Ruby allows us to write it like this:

person.name = "Mary"

Recipe

class MyClass
  def my_attribute=(new_value)
    @my_attribute = new_value
  end
end

As you can see, the parameter can have any name. The important thing is that we assign the parameter to our instance variable.

Full Example

class Person
  # this is the reader
  def email 
    @email
  end
  
  # this is the writer
  def email=(email) 
    @email = email
  end
end

Usually though, you keep method names and instance variables equal.

In Ruby, we calls these concepts attribute readers and writers. Most programming languages call them getters and setters.

Additional Resources

Ruby For Beginners: Attribute writers

What questions do you have?