# :s.respond\_to?(:dup) && :s.dup raises

**URL:** <https://www.ruby-forum.com/t/s-respond-to-dup-s-dup-raises/91224>\
**Category:** Ruby\
**Created:** [April 5, 2007, 7:42pm UTC](https://www.ruby-forum.com/t/s-respond-to-dup-s-dup-raises/91224 "2007-04-05T19:42:18Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![fbeausoleil](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/ec9cab/32.png) [@fbeausoleil](https://www.ruby-forum.com/u/fbeausoleil)\
**Post date:** [April 5, 2007, 7:42pm UTC](https://www.ruby-forum.com/t/s-respond-to-dup-s-dup-raises/91224/1 "2007-04-05T19:42:18Z")

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Hi all !

Symbol lies about it’s ability to respond\_to? to #dup:

irb(main):001:0\> :s.respond\_to?(:dup)  
=\> true  
irb(main):002:0\> :s.dup  
TypeError: can’t dup Symbol  
from (irb):2:in `dup’  
from (irb):2

Fixnum does the same thing. You might argue that the object _can_  
respond to :dup, except it’s simply illegal to respond to it.

Anyway, my feeling is that Symbol and Fixnum (probably Numeric) should  
not respond\_to?(:dup).

Thanks !

---

<div class="post-metadata">

**Author:** ![fbeausoleil](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/ec9cab/32.png) [@fbeausoleil](https://www.ruby-forum.com/u/fbeausoleil)\
**Post date:** [April 5, 2007, 7:55pm UTC](https://www.ruby-forum.com/t/s-respond-to-dup-s-dup-raises/91224/2 "2007-04-05T19:55:37Z")

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François Beausoleil wrote:

> Anyway, my feeling is that Symbol and Fixnum (probably Numeric) should  
> not respond\_to?(:dup).

Here’s a 76-post thread on this very subject, from about six, seven  
weeks ago.

[http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/239426?239426-239938](http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/239426?239426-239938)