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comp.lang.ruby

Range#to_a, each - why inconsistent?

Sergey Volkov

3/29/2006 7:24:00 AM

Could someone explain me, please, why Range with one element is
iterated inconsistently when this element is empty string:

$ irb --simple-prompt
>> ('a'..'a').to_a
=> ["a"]
>> (1..1).to_a
=> [1]
## but:
>> ("".."").to_a
=> []
>> ("".."").each{|s| puts 'Inside'}
=> ""..""
Why to_a returns empty [] and each block never executed?
Is it bug or feature?
Any reasonable explanation?

thanks
Sergey
3 Answers

Robert Dober

3/29/2006 8:09:00 AM

0

On 3/29/06, vsv <gm.vlkv@gmail.com> wrote:
>
> Could someone explain me, please, why Range with one element is
> iterated inconsistently when this element is empty string:
>
> $ irb --simple-prompt
> >> ('a'..'a').to_a
> => ["a"]
> >> (1..1).to_a
> => [1]
> ## but:
> >> ("".."").to_a
> => []
> >> ("".."").each{|s| puts 'Inside'}
> => ""..""
> Why to_a returns empty [] and each block never executed?
> Is it bug or feature?
> Any reasonable explanation?
>
> thanks
> Sergey
>
>
>
Sergey
this looks like a bug to me

as far as I recall the definition of a range,
"" is part of the range ("".."")
I verified with irb and
("".."") === ""
returns true
"" <=> "" returns 0 as expected,
"".succ => "" which is not quite conclusive for me, but see below
anyway it seems inconsistent that
("".."").to_a.include?("") returns false

while
("".."") === "" returns true

No I have mimicked the bahvior with

class NilClass
def succ; nil; end
def <=>(other); 0; end
end

Guess what
(nil..nil).to_a returns ??

[nil] as expected

the behavior you described clearly seems to be a bug.
Regards
Robert

--
Deux choses sont infinies : l'univers et la bêtise humaine ; en ce qui
concerne l'univers, je n'en ai pas acquis la certitude absolue.

- Albert Einstein

Farrel Lifson

3/29/2006 8:11:00 AM

0

I initially thought it was because "".succ == "" which is not correct,
however I created a custom class that returns itself when succ is
called:

class BadSucc
include Comparable
attr_accessor :value
def <=>(other)
self.value <=> other.value
end
def succ
self
end
end

But this did not seem to work
irb(main):002:0> b = BadSucc.new
=> #<BadSucc:0x2dc49a8>
irb(main):003:0> b.value = 1
=> 1
irb(main):008:0> (b..b).to_a
=> [#<BadSucc:0x2dc49a8 @value=1>]

So it seems like it might be a bug to me or there is some other reason
why ("".."").to_a returns empty while (b..b).to_a doesn't.

Farrel

clams_casino

9/2/2008 12:43:00 PM

0

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>the one who is fucked up.
>
>

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His whimsical choice of Palin (at least at this stage of her political
career) sure brings it all into question.