Maintenance Ruby 3.3 gets fixes, but no new features. Switch to Ruby 4.0 →
instance method
BasicObject#__id__
obj.__id__ → integer
obj.object_id → integer
gc.c
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VALUE
rb_obj_id(VALUE obj)
{
/*
* 32-bit VALUE space
* MSB ------------------------ LSB
* false 00000000000000000000000000000000
* true 00000000000000000000000000000010
* nil 00000000000000000000000000000100
* undef 00000000000000000000000000000110
* symbol ssssssssssssssssssssssss00001110
* object oooooooooooooooooooooooooooooo00 = 0 (mod sizeof(RVALUE))
* fixnum fffffffffffffffffffffffffffffff1
*
* object_id space
* LSB
* false 00000000000000000000000000000000
* true 00000000000000000000000000000010
* nil 00000000000000000000000000000100
* undef 00000000000000000000000000000110
* symbol 000SSSSSSSSSSSSSSSSSSSSSSSSSSS0 S...S % A = 4 (S...S = s...s * A + 4)
* object oooooooooooooooooooooooooooooo0 o...o % A = 0
* fixnum fffffffffffffffffffffffffffffff1 bignum if required
*
* where A = sizeof(RVALUE)/4
*
* sizeof(RVALUE) is
* 20 if 32-bit, double is 4-byte aligned
* 24 if 32-bit, double is 8-byte aligned
* 40 if 64-bit
*/
return rb_find_object_id(obj, cached_object_id);
}
Returns an integer identifier for obj.
The same number will be returned on all calls to object_id for a given object, and no two active objects will share an id.
Note: that some objects of builtin classes are reused for optimization. This is the case for immediate values and frozen string literals.
BasicObject implements __id__, Kernel implements object_id.
Immediate values are not passed by reference but are passed by value: nil, true, false, Fixnums, Symbols, and some Floats.
Example
Object.new.object_id == Object.new.object_id # => false (21 * 2).object_id == (21 * 2).object_id # => true "hello".object_id == "hello".object_id # => false "hi".freeze.object_id == "hi".freeze.object_id # => true