Hi all,
Ruby 1.8.2
Consider:
irb(main):001:0> a = []
=> []
irb(main):002:0> a[0..1]
=> []
irb(main):003:0> a[-2..-1]
=> nil
Why does the first return [] and the second return nil?
Regards,
Dan
Hi all,
Ruby 1.8.2
Consider:
irb(main):001:0> a =
=>
irb(main):002:0> a[0..1]
=>
start at a legitimate index and continue with every possible index until the
end, not matter where that is
irb(main):003:0> a[-2..-1]
=> nil
start at a illegitimate index and return that there cannot be anything after
this - ergo 'nil'
Why does the first return and the second return nil?
or at least that makes sense to me...
cheers.
-a
Daniel Berger wrote:
Hi all,
Ruby 1.8.2
Consider:
irb(main):001:0> a =
=>
irb(main):002:0> a[0..1]
=>
irb(main):003:0> a[-2..-1]
=> nilWhy does the first return and the second return nil?
Archive reading:
http://groups.google.com/groups?threadm=BAY22-F7pSWerOc0Ne000000288@hotmail.com
daz
Ara.T.Howard wrote:
···
On Fri, 22 Jul 2005, Daniel Berger wrote:
> Hi all,
>
> Ruby 1.8.2
>
> Consider:
>
> irb(main):001:0> a =
> =>
> irb(main):002:0> a[0..1]
> =>start at a legitimate index and continue with every possible index until the
end, not matter where that is> irb(main):003:0> a[-2..-1]
> => nilstart at a illegitimate index and return that there cannot be anything after
this - ergo 'nil'> Why does the first return and the second return nil?
or at least that makes sense to me...
cheers.
-a
Please explain how one is "legitimate" and the other is not. In both
cases, the indices do not exist.
Regards,
Dan
Then why this?:
irb(main):001:0> [0]
=> nil
irb(main):002:0> [0..1]
=>
irb(main):003:0> [1..1]
=> nil
0 is not a legitimate index on an empty array. Seems like a bug to me.
···
On 7/21/05, Ara.T.Howard <Ara.T.Howard@noaa.gov> wrote:
On Fri, 22 Jul 2005, Daniel Berger wrote:
> Hi all,
>
> Ruby 1.8.2
>
> Consider:
>
> irb(main):001:0> a =
> =>
> irb(main):002:0> a[0..1]
> =>start at a legitimate index and continue with every possible index until the
end, not matter where that is
Hi --
Daniel Berger wrote:
Hi all,
Ruby 1.8.2
Consider:
irb(main):001:0> a =
=>
irb(main):002:0> a[0..1]
=>
irb(main):003:0> a[-2..-1]
=> nilWhy does the first return and the second return nil?
Archive reading:
http://groups.google.com/groups?threadm=BAY22-F7pSWerOc0Ne000000288@hotmail.com
I'll perhaps superfluously report the results of my digging, as long
as I've done it 
See the ruby-talk threads starting at:
10136
24700
84973
In the first of these, Matz talks about the index pointing at an
(imaginary) edge between elements.
David
···
On Fri, 22 Jul 2005, daz wrote:
--
David A. Black
dblack@wobblini.net
yes it does.
-a
···
On Fri, 22 Jul 2005, Jason Foreman wrote:
On 7/21/05, Ara.T.Howard <Ara.T.Howard@noaa.gov> wrote:
On Fri, 22 Jul 2005, Daniel Berger wrote:
Hi all,
Ruby 1.8.2
Consider:
irb(main):001:0> a =
=>
irb(main):002:0> a[0..1]
=>start at a legitimate index and continue with every possible index until the
end, not matter where that isThen why this?:
irb(main):001:0> [0]
=> nil
irb(main):002:0> [0..1]
=>
irb(main):003:0> [1..1]
=> nil0 is not a legitimate index on an empty array. Seems like a bug to me.
--
email :: ara [dot] t [dot] howard [at] noaa [dot] gov
phone :: 303.497.6469
My religion is very simple. My religion is kindness.
--Tenzin Gyatso
===============================================================================
if you are thinking in terms of 'c' - which i tend to - an offset of zero from
a thing is the same as the thing. but that clearly is not what's going on
here. i think you are right to call that a bug.
-a
···
On Fri, 22 Jul 2005, Daniel Berger wrote:
Ara.T.Howard wrote:
On Fri, 22 Jul 2005, Daniel Berger wrote:
Hi all,
Ruby 1.8.2
Consider:
irb(main):001:0> a =
=>
irb(main):002:0> a[0..1]
=>start at a legitimate index and continue with every possible index until the
end, not matter where that isirb(main):003:0> a[-2..-1]
=> nilstart at a illegitimate index and return that there cannot be anything after
this - ergo 'nil'Why does the first return and the second return nil?
or at least that makes sense to me...
cheers.
-a
Please explain how one is "legitimate" and the other is not. In both
cases, the indices do not exist.
--
email :: ara [dot] t [dot] howard [at] noaa [dot] gov
phone :: 303.497.6469
My religion is very simple. My religion is kindness.
--Tenzin Gyatso
===============================================================================
David A. Black wrote:
Hi --
>
> Daniel Berger wrote:
>> Hi all,
>>
>> Ruby 1.8.2
>>
>> Consider:
>>
>> irb(main):001:0> a =
>> =>
>> irb(main):002:0> a[0..1]
>> =>
>> irb(main):003:0> a[-2..-1]
>> => nil
>>
>> Why does the first return and the second return nil?
>>
>
>
> Archive reading:
> http://groups.google.com/groups?threadm=BAY22-F7pSWerOc0Ne000000288@hotmail.comI'll perhaps superfluously report the results of my digging, as long
as I've done it10136
24700
84973In the first of these, Matz talks about the index pointing at an
(imaginary) edge between elements.David
Thanks David and Daz.
Maybe this should go in the FAQ.
Regards,
Dan
···
On Fri, 22 Jul 2005, daz wrote:
I believe that you are intentionally allowed to go 'one past the end' when
taking slices, for convenience/symmetry reasons.
irb(main):001:0> a=["x","y"]
=> ["x", "y"]
irb(main):002:0> a[0]
=> "x"
irb(main):003:0> a[1]
=> "y"
irb(main):004:0> a[2]
=> nil
irb(main):005:0> a[0,1]
=> ["x"]
irb(main):006:0> a[1,1]
=> ["y"]
irb(main):007:0> a[2,1] #<<<< note
=> #<<<<
irb(main):008:0> a[3,1]
=> nil
irb(main):009:0>
It makes sense if you think of:
irb(main):009:0> a[0..-1]
=> ["x", "y"]
irb(main):010:0> a[1..-1]
=> ["y"]
irb(main):011:0> a[2..-1]
=>
as symmetrical to
irb(main):012:0> a[0,2]
=> ["x", "y"]
irb(main):013:0> a[0,1]
=> ["x"]
irb(main):014:0> a[0,0]
=>
That is, a legitimate array slice operation should return an array, and if
the original array is of size N, we can expect a slice of size between 0 and
N. In that case there are N+1 "sensible" starting positions. Any starting
position outside 0..N is considered invalid and returns nil. (Whether that
should actually raise an exception is off-topic
In the case of a zero-sized array (N=0): then index 0 is "one past the end".
irb(main):015:0> [0,1]
=>
irb(main):016:0> [1,1]
=> nil
A bit woolly, but perhaps someone else can put it better.
Regards,
Brian.
···
On Fri, Jul 22, 2005 at 01:20:59PM +0900, Ara.T.Howard wrote:
>Please explain how one is "legitimate" and the other is not. In both
>cases, the indices do not exist.if you are thinking in terms of 'c' - which i tend to - an offset of zero
from
a thing is the same as the thing. but that clearly is not what's going on
here. i think you are right to call that a bug.