Bug #1962: Kernel#Array shouldn't call #to_a if it has been undef'd
http://redmine.ruby-lang.org/issues/show/1962

Author: George Ogata
Status: Open, Priority: Normal
ruby -v: ruby 1.8.6 (2009-08-19 patchlevel 384) [i686-darwin9.7.0]

Applies to 1.8.*.

Kernel#Array is supposed to behave as follows:

 * if the object has a #to_ary, call it and return the result
 * else if the object has a #to_a, call it and return the result
 * else return the object in a 1-element array

If #to_a has been undefined (with #undef_method), however, #Array will see the NULL entry in the method table and try to call it.  This is silly.  Practically speaking, this leads to spurious warnings ("default `to_a' will be obsolete") when calling #Array on an ActiveRecord AssociationProxy.  This happens because AssociationProxy undefs all its methods (including #to_a, since Object#to_a is defined), in order to delegate everything to the object it wraps via #method_missing.  #Array will thus find #to_a to be mapped to an undef'd method, and proceed to call it, which gets delegated to the wrapped object, which doesn't implement #to_a, so it falls back to Object#to_a -- hence the warning.

Aside from finding this behavior strange, I don't really see how ActiveRecord can work around this properly.  I've attached a patch which makes #Array check if the #to_a it found is an undef'd method, and not call it if it is.  This is consistent with 1.9.


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