Ruby类中的super

Question

As I know 'super' calls the method of parent class. Here is a code from jekyll project:

def read_yaml(base, name)
  super(base, name)
  self.extracted_excerpt = extract_excerpt
end

And here is a class declaration:

class Post

There is no parent class. What is the 'super' on this context ?

Here is full class code .

Answer 1

super doesn't just call methods on the parent class but also those in included modules.

The general resolution order is

• instance methods of the eigenclass (or singleton class, which is an alternative name for the same thing) of the object
• instance methods of the object
• methods in any included modules, starting from the last included module
• if not yet found, do all previous steps for the parent class (and then up until a method is found)

In this case, its Convertible#read_yaml .

Answer 2

Including a module adds it as an ancestor of the class, allowing its methods to be called with super . Post includes both Comparable and Convertible , so the super method is in one of those classes.

For example:

module Foo; end
class Bar
  include Foo
end

Bar.ancestors
# [Bar, Foo, Object, Kernel, BasicObject]

Answer 3

In Ruby, the super keyword calls a parent method of the same name using the same arguments.

It can also be used for inherited classes.

Example

class Foo
  def baz(str)
    p 'parent with ' + str
  end
end
class Bar < Foo
  def baz(str)
    super
    p 'child with ' + str
  end
end

Bar.new.baz('test') # => 'parent with test' \ 'child with test'

Super can be called any number of times and can be used in multiple inherited classes.

class Foo
  def gazonk(str)
    p 'parent with ' + str
  end
end

class Bar < Foo
  def gazonk(str)
    super
    p 'child with ' + str
  end
end

class Baz < Bar
  def gazonk(str)
    super
    p 'grandchild with ' + str
  end
end

Baz.new.gazonk('test') # => 'parent with test' \ 'child with test' \ 'grandchild with test'

An exception will be raised if there is no parent method of the same name.

class Foo; end

class Bar < Foo
  def baz(str)
    super
    p 'child with ' + str
  end
end

Bar.new.baz('test') # => NoMethodError: super: no superclass method ‘baz’

Hope this helped.