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Overriding parent's singleton method

1

In C#, a regular class cannot inherit from a static class. A similar case for Ruby seems to be:

class Foo
 class << self
 def test
 "this is test"
 end
 end
end

class Bar < Foo
 def test
 puts super
 end
end

Bar.new.test # >> error

Is there a way for a regular class Bar to inherit from Foo and override test?

ruby

share|improve this question

edited Mar 7 at 7:52

sawa

132k29205305

asked Mar 6 at 17:22

Adrian WydmanskiAdrian Wydmanski

742415

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  There are no static classes in ruby. This inheritance here works just fine. Bar#test fails to find super method because there's none. test that is in Foo lives on another level. Not instances of the class, but the class object itself. Overall, it's not clear what you're trying to ask here.
  
  – Sergio Tulentsev
  Mar 6 at 17:26
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @SergioTulentsev Is there a way for me to call super so that "this is test" would be printed?
  
  – Adrian Wydmanski
  Mar 6 at 17:40
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, define test in Bar the same way, as singleton method. This would make Foo.test its proper super method.
  
  – Sergio Tulentsev
  Mar 6 at 17:41
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  There's nothing wrong with the way you've defined Foo::test (the "::" meaning it's a class method, as opposed to Foo#test if it were an instance method), but the normal (shorthand) way it's written is def self.test; ... ; end (which here is the same as def Foo.test; ... ; end).
  
  – Cary Swoveland
  Mar 6 at 20:39
  
  

  
  
  
  

add a comment | 

1

In C#, a regular class cannot inherit from a static class. A similar case for Ruby seems to be:

class Foo
 class << self
 def test
 "this is test"
 end
 end
end

class Bar < Foo
 def test
 puts super
 end
end

Bar.new.test # >> error

Is there a way for a regular class Bar to inherit from Foo and override test?

ruby

share|improve this question

edited Mar 7 at 7:52

sawa

132k29205305

asked Mar 6 at 17:22

Adrian WydmanskiAdrian Wydmanski

742415

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  There are no static classes in ruby. This inheritance here works just fine. Bar#test fails to find super method because there's none. test that is in Foo lives on another level. Not instances of the class, but the class object itself. Overall, it's not clear what you're trying to ask here.
  
  – Sergio Tulentsev
  Mar 6 at 17:26
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @SergioTulentsev Is there a way for me to call super so that "this is test" would be printed?
  
  – Adrian Wydmanski
  Mar 6 at 17:40
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, define test in Bar the same way, as singleton method. This would make Foo.test its proper super method.
  
  – Sergio Tulentsev
  Mar 6 at 17:41
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  There's nothing wrong with the way you've defined Foo::test (the "::" meaning it's a class method, as opposed to Foo#test if it were an instance method), but the normal (shorthand) way it's written is def self.test; ... ; end (which here is the same as def Foo.test; ... ; end).
  
  – Cary Swoveland
  Mar 6 at 20:39
  
  

  
  
  
  

add a comment | 

In C#, a regular class cannot inherit from a static class. A similar case for Ruby seems to be:

class Foo
 class << self
 def test
 "this is test"
 end
 end
end

class Bar < Foo
 def test
 puts super
 end
end

Bar.new.test # >> error

Is there a way for a regular class Bar to inherit from Foo and override test?

ruby

share|improve this question

edited Mar 7 at 7:52

sawa

132k29205305

asked Mar 6 at 17:22

Adrian WydmanskiAdrian Wydmanski

742415

class Foo
 class << self
 def test
 "this is test"
 end
 end
end

class Bar < Foo
 def test
 puts super
 end
end

Bar.new.test # >> error

share|improve this question

edited Mar 7 at 7:52

sawa

132k29205305

asked Mar 6 at 17:22

Adrian WydmanskiAdrian Wydmanski

742415

share|improve this question

edited Mar 7 at 7:52

sawa

132k29205305

asked Mar 6 at 17:22

Adrian WydmanskiAdrian Wydmanski

742415

edited Mar 7 at 7:52

sawa

132k29205305

edited Mar 7 at 7:52

sawa

132k29205305

asked Mar 6 at 17:22

Adrian WydmanskiAdrian Wydmanski

742415

asked Mar 6 at 17:22

Adrian WydmanskiAdrian Wydmanski

742415

1 Answer
1

active

oldest

votes

1

Is there a way for Bar to inherit from Foo

You've done that part correctly

and override test?

You need to define Bar.test as a class method, but what you have written is an instance method definition (and invocation). Try

class Bar < Foo
 class << self
 def test
 super + ", man"
 end
 end
end

Bar.test
#=> "this is a test, man"

There is no such thing as a static class or method in Ruby, so the instance method invocation Bar.new.test will never refer to the same thing as the class method invocation Bar.test as it might in languages with the concept of static methods.

share|improve this answer

answered Mar 6 at 17:50

Andrew SchwartzAndrew Schwartz

1,85811132

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So the only way to make it work is to make test method inside Bar singleton as well?
  
  – Adrian Wydmanski
  Mar 6 at 18:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, otherwise you're not overriding anything. Another way to see this: Foo.new.test will not call your method defined on the class Foo. (Protip: don't use the name test since that's a method on Kernel so the error messages may be more confusing than they need to be.)
  
  – Andrew Schwartz
  Mar 6 at 21:19
  

  
  
  
  

add a comment | 

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1

Is there a way for Bar to inherit from Foo

You've done that part correctly

and override test?

You need to define Bar.test as a class method, but what you have written is an instance method definition (and invocation). Try

class Bar < Foo
 class << self
 def test
 super + ", man"
 end
 end
end

Bar.test
#=> "this is a test, man"

There is no such thing as a static class or method in Ruby, so the instance method invocation Bar.new.test will never refer to the same thing as the class method invocation Bar.test as it might in languages with the concept of static methods.

share|improve this answer

answered Mar 6 at 17:50

Andrew SchwartzAndrew Schwartz

1,85811132

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So the only way to make it work is to make test method inside Bar singleton as well?
  
  – Adrian Wydmanski
  Mar 6 at 18:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, otherwise you're not overriding anything. Another way to see this: Foo.new.test will not call your method defined on the class Foo. (Protip: don't use the name test since that's a method on Kernel so the error messages may be more confusing than they need to be.)
  
  – Andrew Schwartz
  Mar 6 at 21:19
  

  
  
  
  

add a comment | 

1

Is there a way for Bar to inherit from Foo

You've done that part correctly

and override test?

You need to define Bar.test as a class method, but what you have written is an instance method definition (and invocation). Try

class Bar < Foo
 class << self
 def test
 super + ", man"
 end
 end
end

Bar.test
#=> "this is a test, man"

There is no such thing as a static class or method in Ruby, so the instance method invocation Bar.new.test will never refer to the same thing as the class method invocation Bar.test as it might in languages with the concept of static methods.

share|improve this answer

answered Mar 6 at 17:50

Andrew SchwartzAndrew Schwartz

1,85811132

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  So the only way to make it work is to make test method inside Bar singleton as well?
  
  – Adrian Wydmanski
  Mar 6 at 18:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Yes, otherwise you're not overriding anything. Another way to see this: Foo.new.test will not call your method defined on the class Foo. (Protip: don't use the name test since that's a method on Kernel so the error messages may be more confusing than they need to be.)
  
  – Andrew Schwartz
  Mar 6 at 21:19
  

  
  
  
  

add a comment | 

Is there a way for Bar to inherit from Foo

You've done that part correctly

and override test?

You need to define Bar.test as a class method, but what you have written is an instance method definition (and invocation). Try

class Bar < Foo
 class << self
 def test
 super + ", man"
 end
 end
end

Bar.test
#=> "this is a test, man"

There is no such thing as a static class or method in Ruby, so the instance method invocation Bar.new.test will never refer to the same thing as the class method invocation Bar.test as it might in languages with the concept of static methods.

share|improve this answer

answered Mar 6 at 17:50

Andrew SchwartzAndrew Schwartz

1,85811132

class Bar < Foo
 class << self
 def test
 super + ", man"
 end
 end
end

Bar.test
#=> "this is a test, man"

share|improve this answer

answered Mar 6 at 17:50

Andrew SchwartzAndrew Schwartz

1,85811132

answered Mar 6 at 17:50

Andrew SchwartzAndrew Schwartz

1,85811132

answered Mar 6 at 17:50

Andrew SchwartzAndrew Schwartz

1,85811132