From: Robert Klemme <bob.news@...>
Date: 2005-01-08T22:21:25+09:00
Subject: Re: Construct [*nil] works differently in 1.6 and 1.8


"Gennady Bystritksy" <gfb@tonesoft.com> schrieb im Newsbeitrag 
news:41DF1E8F.7020404@tonesoft.com...
> Hi, rubyists
>
> In ruby 1.6 I use the following quite often to quickly convert to arrays:
>
> a = [ *o ]
>
> If 'o' is already an array, 'a' will be the same.

No, there will be two arrays containing the same references.  Note the 
difference:

>> foo=%w{a b c d}
=> ["a", "b", "c", "d"]
>> foo.id
=> 135018196
>> foo.to_a.id
=> 135018196
>> [*foo].id
=> 135018196

foo#to_a just returns self while [*foo] creates a new array.

> If 'o' is non-nil, 'a' becomes an array with 'o' as a single element. 
> Otherwise, if 'o' is nil, 'a' becomes an empty array. Nice and clean.
>
> However, in 1.8 if 'o' is nil, 'a' becomes an array with a single element 
> nil.

Which is more consistent IMHO.

> In other words:
>   in 1.6 [ *nil ] -> []
>   in 1.8 [ *nil ] -> [ nil ]
>
> Was this incompatibility introduced deliberately or is it a bug that 
> slipped through?

I'd say the 1.6 code is inconsistent and that was fixed in later versions.

> It becomes a problem (or rather inconvenience) in 1.8, as I cannot replace 
> [ *o ] with o.to_a as in 1.6, because ruby 1.8 gives warning "default 
> `to_a' will be obsolete" for instances of user defined classes.

You can easily fix this by

class Object; def to_a; [self] end end

>> Object.new.to_a
=> [#<Object:0x10188a10>]

Note also that there is #to_ary which should be implemented if a class has a 
reasonable array representation:

>> ObjectSpace.each_object(Module){|cl| p cl if cl.instance_methods.include? 
>> "to_ary" }
Array
=> 365

Kind regards

    robert