Inheritance

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: Duck typing and core idioms

Article author: Arthur Isaev