[ruby-core:97896] [Ruby master Bug#16788] T_CLASS counts classes double

Issue #16788 has been reported by ana06 (Ana Maria Martinez Gomez).

----------------------------------------
Bug #16788: T_CLASS counts classes double
https://bugs.ruby-lang.org/issues/16788

* Author: ana06 (Ana Maria Martinez Gomez)
* Status: Open
* Priority: Normal
* ruby -v: 1.9 to master
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
Consider the following code:

``` ruby
h = {}
ObjectSpace.count_objects(h)
puts "Counts: #{ h[:T_CLASS] }, #{ h[:T_ICLASS] }"

objects = []
classes = []
ObjectSpace.each_object(Object){|x| objects << x}
ObjectSpace.each_object(Class){|x| classes << x}

class Test
end

objects2 = []
classes2 = []
ObjectSpace.each_object(Object){|x| objects2 << x}
ObjectSpace.each_object(Class){|x| classes2 << x}

objects_ids = objects.map(&:object_id)
new_objects = objects2.reject { |e| objects_ids.include? e.object_id }

puts "New objects belongs to the classes: #{ new_objects.map(&:class).uniq }"
puts "New classes: #{classes2 - classes}"

h = {}
ObjectSpace.count_objects(h)
puts "Counts: #{ h[:T_CLASS] }, #{ h[:T_ICLASS] }"
```

The result is the following:
```
Counts: 690, 46
New objects belongs to the classes: [Array, Class]
New classes: [Test]
Counts: 692, 46
```

This means that the number of `T_CLASS` is increased by 2 with the creation of 1 class. Why is this the case? Is this a bug?

Consider the slightly modified code with:
``` ruby
class Test
  def self.foo 
  end
end
```
In this case the Singleton class is also created and the results are:

```
Counts: 690, 46
New objects belongs to the classes: [Array, Class]
New classes: [#<Class:Test>, Test]
Counts: 693, 46

```

In this case, `T_CLASS` is increased by 3. So it seems like the issue is only with normal classes and not singleton ones.

From https://stackoverflow.com/questions/61031735
 






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