Bug #937: Recursive Hashes As Keys

• Status: Rejected
• Assignee: mame (Yusuke Endoh)
• Target version: Ruby 1.8.7

[dgtized (Charles Comstock)]

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On 1.8.7 hashes which use themselves as keys appear to lack a meaningful value, yet are stored correctly in the keys and values list.

$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]
$ ruby -e 'h = {}; h[h] = h; p h,h[h],h.keys[0],h.values[0]'
{{...}=>{...}}
nil
{{...}=>{...}}
{{...}=>{...}}

Is this intended behavior or a bug?
=end

[dgtized (Charles Comstock)]

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Forgot to mention that h[h] on 1.8.6 is still h instead of degrading to a nil value.
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[mame (Yusuke Endoh)]

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Hi,

2008/12/28 Charles Comstock [e-mail]:

Bug #937: Recursive Hashes As Keys
http://redmine.ruby-lang.org/issues/show/937

Author: Charles Comstock
Status: Open, Priority: Low
Target version: Ruby 1.8.7

On 1.8.7 hashes which use themselves as keys appear to lack a meaningful value, yet are stored correctly in the keys and values list.

$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]
$ ruby -e 'h = {}; h[h] = h; p h,h[h],h.keys[0],h.values[0]'
{{...}=>{...}}
nil
{{...}=>{...}}
{{...}=>{...}}

Is this intended behavior or a bug?

It's an intended change from 1.8.7. The hash value of h changes
when it is assigned:

$ ruby18 -e 'h = {}; p h.hash; h[h] = h; p h.hash'
0
1

Mutable objects (such as Array and Hash) are basically improper for
a hash key if you may modify them. If it is absolutely necessary,
you can use Hash#rehash:

$ ruby18 -e 'h = {}; h[h] = h; h.rehash; p h[h]'
{{...}=>{...}}

--
Yusuke ENDOH [e-mail]

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[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Rejected
• Assignee set to mame (Yusuke Endoh)

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