[ruby-core:67417] [ruby-trunk - Bug #10713] Assigning default value for a Hash as an empty Array creating unpredictable results

Issue #10713 has been updated by Austin Ziegler.


 It's quite expected because the default array is created exactly once:
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 letters =3D Hash.new([])
 letters.default.object_id # =3D> 70310393550400
 letters[:a].object_id # =3D> 70310393550400
 letters[:b].object_id # =3D> 70310393550400
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 The pattern that Arvinder *wants* is:
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 letters =3D Hash.new { |h, k| h[k] =3D [] }
 letters.default # =3D> nil
 letters.default_proc # =3D> #<Proc:0x007fe4d4099988@(irb):7>
 letters[:a].object_id # =3D> 70310393174180
 letters[:b].object_id # =3D> 70310393171680
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 It's possible to make the correct pattern do the "wrong thing":
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 array =3D []
 array.object_id # =3D> 70310393550400
 letters =3D Hash.new { |h, k| h[k] =3D array }
 letters.default # =3D> nil
 letters.default_proc # =3D> #<Proc:0x007fe4d4099988@(irb):7>
 letters[:a].object_id # =3D> 70310393550400
 letters[:b].object_id # =3D> 70310393550400
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 -a
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 On Wed, Jan 7, 2015 at 8:16 PM, <[e-mail]> wrote:
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 > Issue #10713 has been updated by Martin D=C3=BCrst.
 >
 >
 > Hiroshi SHIBATA wrote:
 > > It's expected behavior
 >
 > Hiroshi, can you tell us why it's expected behavior? It looks quite
 > surprising.
 >
 > ----------------------------------------
 > Bug #10713: Assigning default value for a Hash as an empty Array creating
 > unpredictable results
 > https://bugs.ruby-lang.org/issues/10713#change-50846
 >
 > * Author: Arvinder Singh
 > * Status: Rejected
 > * Priority: Normal
 > * Assignee:
 > * Category: core
 > * Target version: current: 2.2.0
 > * ruby -v: ruby 2.2.0p0 (2014-12-25 revision 49005) [x86_64-darwin14]
 > * Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
 > ----------------------------------------
 > Creating a Hash with a default value works fine, unless the default value
 > is an empty Array.
 >
 > E.g. the following returns an empty Hash...
 >
 > ~~~
 > irb(main):001:0> letters =3D Hash.new([])
 > =3D> {}
 > irb(main):002:0> letters[:a] << 1
 > =3D> [1]
 > irb(main):003:0> letters[:a] << 2
 > =3D> [1, 2]
 > irb(main):004:0> letters[:a]
 > =3D> [1, 2]
 > irb(main):005:0> letters
 > =3D> {}
 > ~~~
 >
 > whereas the following code explicitly defining hash keys works.
 >
 > ~~~
 > irb(main):001:0> letters =3D {a: [], b: []}
 > =3D> {:a=3D>[], :b=3D>[]}
 > irb(main):002:0> letters[:a] << 1
 > =3D> [1]
 > irb(main):003:0> letters[:a] << 2
 > =3D> [1, 2]
 > irb(main):004:0> letters[:a]
 > =3D> [1, 2]
 > irb(main):005:0> letters
 > =3D> {:a=3D>[1, 2], :b=3D>[]}
 > ~~~
 >
 > Is this an unpredictable(bug) or an expected behavior(feature). I tend to
 > lean towards the former, but I might be wrong.
 >
 >
 >
 > --
 > https://bugs.ruby-lang.org/
 >
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 Austin Ziegler * [e-mail] * [e-mail]
 http://www.halostatue.ca/ * http://twitter.com/halostatue

----------------------------------------
Bug #10713: Assigning default value for a Hash as an empty Array creating u=
npredictable results
https://bugs.ruby-lang.org/issues/10713#change-50848

* Author: Arvinder Singh
* Status: Rejected
* Priority: Normal
* Assignee:=20
* Category: core
* Target version: current: 2.2.0
* ruby -v: ruby 2.2.0p0 (2014-12-25 revision 49005) [x86_64-darwin14]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
Creating a Hash with a default value works fine, unless the default value i=
s an empty Array.

E.g. the following returns an empty Hash...

~~~
irb(main):001:0> letters =3D Hash.new([])
=3D> {}
irb(main):002:0> letters[:a] << 1
=3D> [1]
irb(main):003:0> letters[:a] << 2
=3D> [1, 2]
irb(main):004:0> letters[:a]
=3D> [1, 2]
irb(main):005:0> letters
=3D> {}
~~~

whereas the following code explicitly defining hash keys works.

~~~
irb(main):001:0> letters =3D {a: [], b: []}
=3D> {:a=3D>[], :b=3D>[]}
irb(main):002:0> letters[:a] << 1
=3D> [1]
irb(main):003:0> letters[:a] << 2
=3D> [1, 2]
irb(main):004:0> letters[:a]
=3D> [1, 2]
irb(main):005:0> letters
=3D> {:a=3D>[1, 2], :b=3D>[]}
~~~

Is this an unpredictable(bug) or an expected behavior(feature). I tend to l=
ean towards the former, but I might be wrong.



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https://bugs.ruby-lang.org/