immutable arrays: Unexpected resutls in trivial test

[djcoin]

First, thanks for your library !

Well, then i'm having a hard time using arrays.
Here are so crucial points that I think I did not quite get how immutable arrays are supposed to work :

• array's length
  the array length is not correct, eg:

  im.array([1, 2]).dissoc(1).length => 2
  im.array([1, 2]).dissoc(1).toJSON() => [ 1 ]

  And "im.array([1, 2]).dissoc(0).get(0)" does not work (undefined).
  So in my code for example I'm not able to pick values one by one until the array is finished as I don't know how to check for emptyness.

• dissoc
  array.dissoc leaves a "hole", eg:

  im.array([1, 2, 3, 4, 5]).dissoc(2).toJSON() => [ 1, 2, , 4, 5 ] )
  ( leading to ~ same behaviour as array.assoc(2, null) which would be ok. )
  To me but I may be mistaken, creating an array and then dissoc an elem at index i
  should be the same as creating from the start an array without this elem at index i.

Thanks for any insights

A bunch of test

Using a simple immutable array [ 5, 6 ]:

JSON.stringify(im.array([ 5, 6 ])) => '[5,6]'
ok

JSON.stringify(im.array([ 5, 6 ]).dissoc(1)) => '[5]'
ok

JSON.stringify( (im.array([ 5, 6 ]).dissoc(0)).get(0) ) => undefined
I would have expected 6 ( im.array(6).get(0) )

JSON.stringify( (im.array([ 5, 6 ]).dissoc(0)).get(1) ) => '6'
Would have expected undefined ( im.array(6).get(1) )

JSON.stringify( (im.array([ 5, 6 ]).dissoc(1)).get(0) ) => '5'
ok

JSON.stringify( (im.array([ 5, 6 ]).dissoc(1)).get(1) ) => undefined
ok

JSON.stringify(im.array([ 5, 6 ]).dissoc(0)) => '[null,6]'
I would have expected '[ 6 ]' ( JSON.stringify(im.array([ 6 ])) )

[pk11]

this behavior is actually consistent with mutable Array.delete. You could filter out undefined elements for the cost of O(n) like:
im.array([1,2,3]).dissoc(0).filter(function(e) {return e != undefined}).toJSON(); // [ 2, 3 ]