Ruby Language Inheritance What is inherited?
Example
Methods are inherited
class A
def boo; p 'boo' end
end
class B < A; end
b = B.new
b.boo # => 'boo'
Class methods are inherited
class A
def self.boo; p 'boo' end
end
class B < A; end
p B.boo # => 'boo'
Constants are inherited
class A
WOO = 1
end
class B < A; end
p B::WOO # => 1
But beware, they can be overridden:
class B
WOO = WOO + 1
end
p B::WOO # => 2
Instance variables are inherited:
class A
attr_accessor :ho
def initialize
@ho = 'haha'
end
end
class B < A; end
b = B.new
p b.ho # => 'haha'
Beware, if you override the methods that initialize instance variables without calling super, they will be nil. Continuing from above:
class C < A
def initialize; end
end
c = C.new
p c.ho # => nil
Class instance variables are not inherited:
class A
@foo = 'foo'
class << self
attr_accessor :foo
end
end
class B < A; end
p B.foo # => nil
# The accessor is inherited, since it is a class method
#
B.foo = 'fob' # possible
Class variables aren't really inherited
They are shared between the base class and all subclasses as 1 variable:
class A
@@foo = 0
def initialize
@@foo += 1
p @@foo
end
end
class B < A;end
a = A.new # => 1
b = B.new # => 2
So continuing from above:
class C < A
def initialize
@@foo = -10
p @@foo
end
end
a = C.new # => -10
b = B.new # => -9
