From: merch-redmine@...
Date: 2020-04-15T17:45:36+00:00
Subject: [ruby-core:97897] [Ruby master Bug#16788] T_CLASS counts classes	double

Issue #16788 has been updated by jeremyevans0 (Jeremy Evans).

ruby -v changed from 1.9.3 to master to 1.9 to master
Status changed from Open to Rejected

This is expected and not a bug.  Creating a class automatically creates a singleton class.  Output from debugger when doing `c = Class.new`:

```
#0  class_alloc (flags=0, klass=120258865952) at class.c:172
#1  0x0000073abf1eadcd in rb_class_boot (super=0) at class.c:211
#2  0x0000073abf38971f in rb_class_s_alloc (klass=7951766573360) at object.c:1976
#3  0x0000073abf38a6cf in class_call_alloc_func (allocator=0x73abf389700 <rb_class_s_alloc>, klass=7951766573360) at object.c:2158
#4  0x0000073abf381383 in rb_class_alloc (klass=7951766573360) at object.c:2130
#5  0x0000073abf389549 in rb_class_s_new (argc=0, argv=0x73b07f5f040, klass=7951766573360) at object.c:2210
```

```
#0  class_alloc (flags=52, klass=11142131147240033036) at class.c:172
#1  0x0000073abf1eadcd in rb_class_boot (super=52) at class.c:211
#2  0x0000073abf1ecb73 in make_metaclass (klass=7949829093040) at class.c:502
#3  0x0000073abf1ecb18 in rb_make_metaclass (obj=7949829093040, unused=7950433580800) at class.c:591
#4  0x0000073abf3896b8 in rb_class_initialize (argc=0, argv=0x73b07f5f040, klass=7949829093040) at object.c:2075
```

Referencing the singleton class of a class automatically creates a singleton class of that singleton class.  Output from debugger when doing `c.singleton_class`:

```
#0  class_alloc (flags=52, klass=8589934593) at class.c:172
#1  0x0000073abf1eadcd in rb_class_boot (super=52) at class.c:211
#2  0x0000073abf1ecb73 in make_metaclass (klass=7949829093000) at class.c:502
#3  0x0000073abf1f0024 in rb_singleton_class (obj=7949829093040) at class.c:1803
#4  0x0000073abf38660f in rb_obj_singleton_class (obj=7949829093040) at object.c:325
```

This explains why you get 2 new classes for every class, and 3 if you reference the singleton class.

----------------------------------------
Bug #16788: T_CLASS counts classes double
https://bugs.ruby-lang.org/issues/16788#change-85120

* Author: ana06 (Ana Maria Martinez Gomez)
* Status: Rejected
* 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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