Range#to_a, each - why inconsistent?


#1

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


#2

On 3/29/06, vsv removed_email_address@domain.invalid wrote:

(""…"").to_a

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

#3

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