Inheritance
| Inherit with < | |
| Call super | |
| The ancestors chain | |
| Override carefully |
Inherit with <
Write the child class name, then the < sign, then the parent class name. The child receives every method of the parent and can add its own.
If classes are new to you, start with
Classes and objects.
class Animal
def speak
puts "Some sound"
end
end
class Dog < Animal
end
Dog.new.speak
Call super
When a child defines a method with the same name, the child version wins. Call super inside it to run the parent version as well.
Plain super passes the same arguments along. Add explicit arguments in parentheses when the parent needs different ones.
class Dog < Animal
def speak
puts "Dog says:"
super
end
end
The ancestors chain
Every class remembers its full lookup path. Ask ancestors to see the class itself, then included modules, then the parent, up to Object and BasicObject.
Ruby walks this list from left to right when you call a method, and the first match runs. For Dog it prints Dog, Animal, Object, Kernel, BasicObject.
puts Dog.ancestors.inspect
Override carefully
Override only when the child truly behaves differently. Keep the method name and argument shape so old callers keep working.
If the parent method does useful work, call super instead of copying its code. Duplicated logic drifts apart over time.
class Cat < Animal
def speak
puts "Meow"
end
end
Cat.new.speak
Next: Enumerables
Article author: Arthur Isaev