[ruby-core:98306] [Ruby master Bug#16850] Object#hash doesn't behave as documented
Issue #16850 has been updated by Dan0042 (Daniel DeLorme).
Would it be feasible to raise some sort of error when trying to redefine Integer#hash ?
Not just for this case, but I feel there were other cases where ruby bypasses the method call to use the built-in implementation directly. Can't recall exactly atm.
Making certain methods un-overridable could be a useful signal that "this is not going to work as you expect".
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Bug #16850: Object#hash doesn't behave as documented
https://bugs.ruby-lang.org/issues/16850#change-85544
* Author: ana06 (Ana Maria Martinez Gomez)
* Status: Open
* Priority: Normal
* ruby -v: master
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
From [Ruby 2.7 Object class documentation](https://ruby-doc.org/core-2.7.0/Object.html#method-i-hash):
>The hash value is used along with eql? by the Hash class to determine if two objects reference the same hash key.
From this I expect that overwritting the `Object#hash` method changes the Hashing algorithm. But this is only the case for some objets. Consider the following code:
```Ruby
class Object
def hash
i_dont_exist
end
end
class Ana
end
hash = {}
hash[3] = true
hash[3] = false
puts 'Integers are not using the new hash method'
hash[Ana.new] = true
puts 'this will not be executed because the class Ana uses the new hash method'
```
The output of executing this code is:
```
Integers are not using the new hash method
Traceback (most recent call last):
1: from a.rb:13:in `<main>'
a.rb:3:in `hash': undefined local variable or method `i_dont_exist' for #<Ana:0x000055626f0b7a30> (NameError)
```
This proves that Integer hash method is not used to determine if two objects reference the same hash key, as said in the documentation. Check the [`any_hash` method](https://github.com/ruby/ruby/blob/master/hash.c#L188) for the other classes affected.
I think that either the behavior should be modified (aiming for a consistency along different classes and following the documentation) or the documentation updated.
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