Different super() behavior for store() and =[]() in Hash subclass

[billmcn]

I created a simple class that subclasses the Hash item assignment. The
super function does differernt things depending on whether I use the
store or []= function. For example, this code works

class GoodHashSubclass < Hash
def store(item, value)
super.store(item, value)
end
end

good = GoodHashSubclass.new
good["dog"] = 5
puts good.inspect

It prints {"dog"=>5} as I would expect.

This code--which differs only in that I use []= instead of store--does
not work.

class BadHashSubclass < Hash
def []=(item, value)
super.store(item, value)
end
end

bad = BadHashSubclass.new
bad["dog"] = 5
puts bad.inspect

The BadHashSubclass code generates the following error

./subhash.rb:11:in `[]=': undefined method `store' for 5:Fixnum
(NoMethodError)

For some reason super is finding the superclass of the value 5 rather
than the superclass of self. This looks wrong to me. Is this the
expected behavior?

Thanks.
--wpm

 

[Marcin Mielżyński]

I created a simple class that subclasses the Hash item assignment. The
super function does differernt things depending on whether I use the
store or []= function. For example, this code works

class GoodHashSubclass < Hash
def store(item, value)
super.store(item, value)
end
end

good = GoodHashSubclass.new
good["dog"] = 5
puts good.inspect

It prints {"dog"=>5} as I would expect.

This code--which differs only in that I use []= instead of store--does
not work.

class BadHashSubclass < Hash
def []=(item, value)
super.store(item, value)
end
end

bad = BadHashSubclass.new
bad["dog"] = 5
puts bad.inspect

The BadHashSubclass code generates the following error

./subhash.rb:11:in `[]=': undefined method `store' for 5:Fixnum
(NoMethodError)

You will get the same error trying:

super.[]=(item, value)


The reason is that without parameters super calls superclass method with
the same name passing all parameters by default. Store and []= methods
(they are the same, see in hash.c) return value given as a parameter (in
your case 5)

lopex

 

[billmcn]

That makes sense. Thanks.

I created a simple class that subclasses the Hash item assignment. The
super function does differernt things depending on whether I use the
store or []= function. For example, this code works

class GoodHashSubclass < Hash
def store(item, value)
super.store(item, value)
end
end

good = GoodHashSubclass.new
good["dog"] = 5
puts good.inspect

It prints {"dog"=>5} as I would expect.

This code--which differs only in that I use []= instead of store--does
not work.

class BadHashSubclass < Hash
def []=(item, value)
super.store(item, value)
end
end

bad = BadHashSubclass.new
bad["dog"] = 5
puts bad.inspect

The BadHashSubclass code generates the following error

./subhash.rb:11:in `[]=': undefined method `store' for 5:Fixnum
(NoMethodError)

You will get the same error trying:

super.[]=(item, value)


The reason is that without parameters super calls superclass method with
the same name passing all parameters by default. Store and []= methods
(they are the same, see in hash.c) return value given as a parameter (in
your case 5)

lopex