Let's say we have a loop that enters Association
s to a Dictionary
in a clear order:
| d |
d := Dictionary new: 10.
1 to: 10 do: [ :i |
d add: i -> (i + 9 printStringBase: 20)
].
d
When I evaluate this code I get a Dictionary
in a "twisted" order:
9 -> I
5 -> E
1 -> A
10 ->J
6 -> F
2 -> B
7 -> G
3 -> C
8 -> H
4 -> D
Each time a Dictionary
with the same entry data is created it have the same order, so I assume it is a feature not a bug ..?
I use Pharo v9.0.21.
In addition to this other answer is is worth explaining the apparent disorder shown in the question.
Firstly observe that Dictionary new: 10
will create a new instance of Dictionary
with capacity for a prime number p
of associations greater than 10
. Say 11, 13, 17, whatever.
Secondly, for every association added, the dictionary will compute the hash value of the key and deduce the location from its remainder modulo p
.
Since all keys occurring in the example are instances of SmallInteger
, their hashes will be themselves(*). And since these are smaller than p
, they will equal the modulo and hence be stored in the slots derived from their values in some implementation-dependent way.
Finally, the printing method is free to enumerate the associations in any order.
(*) While this is true in some dialects, I've checked in Pharo and this is not true, 3 hash
is not 3
etc. which explains the "twisting" in the case of Pharo.