From: Aaron Patterson <tenderlove@...>
Date: 2012-05-04T00:23:20+09:00
Subject: [ruby-core:44850] Re: help understanding weird bug


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On Thu, May 03, 2012 at 08:56:42PM +0900, Rodrigo Rosenfeld Rosas wrote:
> Here is a sample application:
>=20
> https://github.com/rosenfeld/weird-sequel-bug
>=20
> And here is the strange behavior:
>=20
> https://github.com/rosenfeld/weird-sequel-bug/blob/master/example.rb
>=20
> children =3D Sq::Node[1].children
> p children.class
> parent =3D children.first.parent
> p children.map &:id
> 2.times { p children.map{|c| c.parent =3D parent; c.id} }
>=20
> Output:
>=20
> Array
> [2, 3]
> [2, 2]
> [3, 3]
>=20
> For some strange reason, changing the parent of the element inside
> children.map{} block will modify the children array itself.
>=20
> for example:
>=20
> p children.map &:id
> children[0].parent =3D parent
> p children.map &:id
>=20
> outputs:
> [2, 3]
> [3, 2]
>=20
> Maybe this is a Sequel bug (I didn't look for the code of
> associations yet), but I'd like to understand how this could happen
> in Ruby.
>=20
> For example, how can I know if this is an ordinary Array or not?
> children.class is Array, so how can I differentiate it from a normal
> Array.

Checking the class is a good start, but I would also check the ancestors
in case anything has been mixed in:

    irb(main):001:0> x =3D []
    =3D> []
    irb(main):002:0> x.extend(Module.new { def [](z); 'hi'; end })
    =3D> []
    irb(main):003:0> x.class
    =3D> Array
    irb(main):004:0> x[1]
    =3D> "hi"
    irb(main):005:0> class << x; self; end.ancestors
    =3D> [#<Module:0x007fd4a9841630>, Array, Enumerable, Object, Kernel, Ba=
sicObject]
    irb(main):006:0>

That said, for better help, you should send this to ruby-talk or the
sequel list.

--=20
Aaron Patterson
http://tenderlovemaking.com/

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