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comp.lang.ruby

Construct [*nil] works differently in 1.6 and 1.8

Gennady

1/7/2005 11:43:00 PM

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. 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.

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?

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.

Thanks in advance,
Gennady.
12 Answers

Pit Capitain

1/8/2005 6:33:00 AM

0

Gennady Bystritksy schrieb:
> 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. 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.

Hi Gennady,

you can use the method "Array":

p Array( [ 1, 2, 3, ] )
p Array( "x" )
p Array( nil )

results in

[1, 2, 3]
["x"]
[]

Regards,
Pit

Gennady

1/8/2005 8:18:00 AM

0

Hi, Pit

I have checked that Array(nil) works fine both in 1.6 and 1.8, thanks
for the tip. Nevertheless, [ *o ] feels so much more attractive ;-).
And I still do not see the reason for the behavior being changed. Is
there any?

Thank you very much,
Gennady.

On Jan 7, 2005, at 10:32 PM, Pit Capitain wrote:

> Gennady Bystritksy schrieb:
>> 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. 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.
>
> Hi Gennady,
>
> you can use the method "Array":
>
> p Array( [ 1, 2, 3, ] )
> p Array( "x" )
> p Array( nil )
>
> results in
>
> [1, 2, 3]
> ["x"]
> []
>
> Regards,
> Pit
>
>

Sincerely,
Gennady Bystritsky

Robert Klemme

1/8/2005 1:19:00 PM

0


"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

Christian Neukirchen

1/9/2005 11:04:00 AM

0

Pit Capitain <pit@capitain.de> writes:

> Hi Gennady,
>
> you can use the method "Array":
>
> p Array( [ 1, 2, 3, ] )
> p Array( "x" )
> p Array( nil )
>
> results in
>
> [1, 2, 3]
> ["x"]
> []
>
> Regards,
> Pit

Hello,

do you maybe also know a nice trick to make it a single-element Array
iff it's not already an Array?

irb(main):001:0> Array("foo\nbar")
=> ["foo\n", "bar"]

This "feature" gives me the creeps.

Christian Neukirchen
<chneukirchen@gmail.com>

Pit Capitain

1/9/2005 12:15:00 PM

0

Christian Neukirchen schrieb:
> do you maybe also know a nice trick to make it a single-element Array
> iff it's not already an Array?
>
> irb(main):001:0> Array("foo\nbar")
> => ["foo\n", "bar"]
>
> This "feature" gives me the creeps.

I didn't know this behavior before, but it is documented. I think you have to
define your own method. If you need an example, let me know.

Regards,
Pit

Robert Klemme

1/9/2005 4:57:00 PM

0


"Christian Neukirchen" <chneukirchen@gmail.com> schrieb im Newsbeitrag
news:m2pt0eeubv.fsf@lilith.local...
> Pit Capitain <pit@capitain.de> writes:
>
>> Hi Gennady,
>>
>> you can use the method "Array":
>>
>> p Array( [ 1, 2, 3, ] )
>> p Array( "x" )
>> p Array( nil )
>>
>> results in
>>
>> [1, 2, 3]
>> ["x"]
>> []
>>
>> Regards,
>> Pit
>
> Hello,
>
> do you maybe also know a nice trick to make it a single-element Array
> iff it's not already an Array?
>
> irb(main):001:0> Array("foo\nbar")
> => ["foo\n", "bar"]

>> ["foo\nbar"]
=> ["foo\nbar"]

Regards

robert

Christian Neukirchen

1/9/2005 6:01:00 PM

0

"Robert Klemme" <bob.news@gmx.net> writes:

> "Christian Neukirchen" <chneukirchen@gmail.com> schrieb im Newsbeitrag
> news:m2pt0eeubv.fsf@lilith.local...
>>
>> Hello,
>>
>> do you maybe also know a nice trick to make it a single-element Array
>> iff it's not already an Array?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> irb(main):001:0> Array("foo\nbar")
>> => ["foo\n", "bar"]
>
>>> ["foo\nbar"]
> => ["foo\nbar"]

irb(main):001:0> a = [1,2,3]
=> [1, 2, 3]
irb(main):002:0> [a]
=> [[1, 2, 3]]

:)

> Regards
>
> robert

Christian Neukirchen
<chneukirchen@gmail.com>

Christian Neukirchen

1/9/2005 6:02:00 PM

0

Pit Capitain <pit@capitain.de> writes:

> Christian Neukirchen schrieb:
>> do you maybe also know a nice trick to make it a single-element Array
>> iff it's not already an Array?
>> irb(main):001:0> Array("foo\nbar")
>> => ["foo\n", "bar"]
>> This "feature" gives me the creeps.
>
> I didn't know this behavior before, but it is documented.

I know.

> I think you
> have to define your own method. If you need an example, let me know.
>
> Regards,
> Pit

Thanks, I can do that on my own... it's just that I found this
behavior, albeit somehow logical, very confusing in the past.

Christian Neukirchen
<chneukirchen@gmail.com>

Robert Klemme

1/9/2005 9:43:00 PM

0


"Christian Neukirchen" <chneukirchen@gmail.com> schrieb im Newsbeitrag
news:m2hdlqeb11.fsf@lilith.local...
> "Robert Klemme" <bob.news@gmx.net> writes:
>
>> "Christian Neukirchen" <chneukirchen@gmail.com> schrieb im Newsbeitrag
>> news:m2pt0eeubv.fsf@lilith.local...
>>>
>>> Hello,
>>>
>>> do you maybe also know a nice trick to make it a single-element Array
>>> iff it's not already an Array?
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Ooops, sorry, I overread that. Then of course my proposal is not a
solution.

Btw, for what do you need that? Just curious...

Kind regards

robert

Christian Neukirchen

1/10/2005 1:38:00 PM

0

"Robert Klemme" <bob.news@gmx.net> writes:

> "Christian Neukirchen" <chneukirchen@gmail.com> schrieb im Newsbeitrag
> news:m2hdlqeb11.fsf@lilith.local...
>> "Robert Klemme" <bob.news@gmx.net> writes:
>>
>>> "Christian Neukirchen" <chneukirchen@gmail.com> schrieb im Newsbeitrag
>>> news:m2pt0eeubv.fsf@lilith.local...
>>>>
>>>> Hello,
>>>>
>>>> do you maybe also know a nice trick to make it a single-element Array
>>>> iff it's not already an Array?
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Ooops, sorry, I overread that. Then of course my proposal is not a
> solution.
>
> Btw, for what do you need that? Just curious...

I needed that rather often for convenience stuff (pass a single
argument or a whole array of them etc.).

When I used [*ary] to do that, I had some "mysterious bugs" that only
appeared if the particular string had a newline in it... it really
took me some time to find those bugs.

> Kind regards
>
> robert

Christian Neukirchen
<chneukirchen@gmail.com>