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Bug #13397

closed

#object_id should not be signed

Added by vo.x (Vit Ondruch) over 4 years ago. Updated over 1 year ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Target version:
-
ruby -v:
ruby 2.4.0p0 (2016-12-24 revision 57164) [i386-linux]
[ruby-core:80545]
Tags:

Description

It is surprising that #object_id returns signed value. Let me explain show two examples. Working with 32b Ruby (ruby 2.4.0p0 (2016-12-24 revision 57164) [i386-linux]) to make this issue more apparent.

$ ruby << \EOR
GC.disable
3_000_000.times { p Object.new.inspect }
EOR
"#<Object:0x57d49a5c>"
"#<Object:0x57d499a8>"
"#<Object:0x57d49930>"
"#<Object:0x57d498b8>"

... snip ...

"#<Object:0x828bf164>"
"#<Object:0x828bf0ec>"
"#<Object:0x828bf074>"
"#<Object:0x828beffc>"
"#<Object:0x828bef84>"
^C-:2:in `p': Interrupt
    from -:2:in `block in <main>'
    from -:2:in `times'
    from -:2:in `<main>'
"#<Object:0x8290b1f4>"

In this example, the "object_id", which is part of the inspect object is unsigned, since it is printed using C sprintf with %p format. There are other libraries, which tries to mimic the output [ 1 ]. The implementation is approximately following:

$ ruby << \EOR
GC.disable
class A
  DEFAULT_OBJ_ID_STR_WIDTH = 0.size == 4 ? 7 : 14

  def inspect
    id_str = (object_id << 1).to_s(16).rjust(DEFAULT_OBJ_ID_STR_WIDTH, '0') 
    "#<#{self.class.name}:0x#{id_str}>"
  end
end
3_000_000.times { p A.new.inspect }
EOR

"#<A:0x58585428>"
"#<A:0x585852d4>"
"#<A:0x585851bc>"
"#<A:0x5858507c>"
"#<A:0x58584ec4>"
"#<A:0x58584d5c>"
"#<A:0x58584c1c>"
"#<A:0x58584adc>"

... snip ...

"#<A:0x7fff4888>"
"#<A:0x7fff47c0>"
"#<A:0x7fff46f8>"
"#<A:0x7fff4630>"
"#<A:0x7fff4568>"
"#<A:0x7fff44a0>"
"#<A:0x7fff43d8>"
"#<A:0x7fff4310>"
"#<A:0x7fff4248>"
"#<A:0x7fff4180>"
"#<A:0x7fff40b8>"
"#<A:0x-7fffc034>"
"#<A:0x-7fffc110>"
"#<A:0x-7fffc1ec>"
"#<A:0x-7fffc2c8>"
"#<A:0x-7fffc3a4>"
"#<A:0x-7fffc480>"
"#<A:0x-7fffc55c>"
"#<A:0x-7fffc638>"
^C-:10:in `p': Interrupt
    from -:10:in `block in <main>'
    from -:10:in `times'
    from -:10:in `<main>'

And the output is quite surprising to me. Why the object_id should be signed value? It doesn't make any sense to me. Is this implementation wrong or is Ruby wrong?

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