From: Dave Burt <dave@...>
Date: 2006-06-03T22:34:10+09:00
Subject: Re: []= and two dimensional arrays

Son SonOfLilit wrote:
> Oi, got that all wrong. Correct version:
> 
> I expect:
>> irb(main):002:0> a = Array.new.fill(Array.new.fill("x", 0, 4), 0, 4)
>> => [["x", "x", "x", "x"], ["x", "x", "x", "x"], ["x", "x", "x", "x"],
>> ["x", "x", "x", "x"]]
>> irb(main):003:0> p a
>> [["x", "x", "x", "x"], ["x", "x", "x", "x"], ["x", "x", "x", "x"], ["x",
>> "x", "x", "x"]]
>> => nil
>> irb(main):004:0> a[2][3] = "a"
>> => "a"
>> irb(main):005:0> p a
>> [["x", "x", "x", "x"], ["x", "x", "x", "x"], ["x", "x", "x", "x"], ["x",
>> "x", "x", "a"]]
>> => nil
>> irb(main):006:0>
>>
>> ========================
>>
>> I get:
>> irb(main):002:0> a = Array.new.fill(Array.new.fill("x", 0, 4), 0, 4)
>> => [["x", "x", "x", "x"], ["x", "x", "x", "x"], ["x", "x", "x", "x"],
>> ["x", "x",
>>  "x", "x"]]
>> irb(main):003:0> p a
>> [["x", "x", "x", "x"], ["x", "x", "x", "x"], ["x", "x", "x", "x"], ["x",
>> "x", "x
>> ", "x"]]
>> => nil
>> irb(main):004:0> a[2][3] = "a"
>> => "a"
>> irb(main):005:0> p a
>> [["x", "x", "x", "a"], ["x", "x", "x", "a"], ["x", "x", "x", "a"], ["x",
>> "x", "x
>> ", "a"]]
>> => nil
>>
>> =========================
>>
>> I spend hours debugging and when I find it out, I have no clue how to
>> solve it.
>>
>> Could somebody clue me as to a solution?

OK, here's the clue. You only have two arrays. Scroll down for spoilers.



































OK, here's the key.

  a = Array.new.fill(Array.new.fill("x", 0, 4), 0, 4)

1) create an array (the inner "Array.new")
2) fill it with 4 "x"s
3) create another array (the outer "Array.new")
4) fill it with 4 references to the first array

What you want is probably:

  a = Array.new(4) { Array.new(4, "x") }

or

  a = Array.new(4) { Array.new(4) { "x" }}

That will create a new array for each of the four elements it
initializes the outer array with.

The second version will give you 16 strings instead of just 4.

Cheers,
Dave