The set is built as a number of key-value pairs of the hash and the object.
When you modify the object the key that contains the hash does not get
updated. A good reason not to put mutables in sets.
On Tuesday, December 15, 2015 at 5:17:00 PM UTC+1, Josh Langsfeld wrote:
>
> I played with it a bit more and am seeing some unexpected behavior. If you
> add a mutable element, change it, and then add another equal one, the set
> gets two elements. But if you don't mutate the element, it stays at one.
>
> julia> s = Set{Vector{Int}}()
> Set{Array{Int64,1}}()
>
> julia> el = [1,2,3]; push!(s, el)
> Set([[1,2,3]])
>
> julia> push!(s, [1,2,3]) #Pushing a new array object, but the length
> stays at 1.
> Set([[1,2,3]])
>
> julia> s = Set{Vector{Int}}()
> Set{Array{Int64,1}}()
>
> julia> el = [1,2,3]; push!(s, el)
> Set([[1,2,3]])
>
> julia> el[1] = 10; @show s; #Mutate the set element from the outside
> s = Set([[10,2,3]])
>
> julia> push!(s, [10,2,3])
> Set([[10,2,3],[10,2,3]])
>
> julia> length(s)
> 2
>
> julia> els = collect(s); els[1] == els[2]
> true
>
> Is something buggy going on here?
>
> On Tuesday, December 15, 2015 at 10:57:31 AM UTC-5, Josh Langsfeld wrote:
>>
>> It's not array equality that's the issue here. Arrays with the same
>> elements are '==' (but not '==='). If you manually test pushing the same
>> array to a Set you'll see it works fine.
>>
>> Jan, what happened is that your 'santa' function modifies and returns the
>> same array that was passed in instead of creating a new one. So the only
>> array that ever gets created is the first 'start = [0 0]' and it just gets
>> continually modified, both in the santa function and in the set. Switching
>> to a tuple works because you are forced to create a new tuple to change one
>> of the elements.
>>
>> On Tuesday, December 15, 2015 at 3:32:40 AM UTC-5, Tomas Lycken wrote:
>>>
>>> Probably because the arrays will not be equal even if their contents are
>>> equal (this is true of most mutable types in Julia).
>>>
>>> If you try representing a position as a tuple `(0,0)` instead of as an
>>> array `[0,0]`, you'll find that it works as expected.
>>>
>>> // T
>>>
>>> On Tuesday, December 15, 2015 at 8:28:36 AM UTC+1, Jan Strube wrote:
>>>>
>>>> That's not a problem at all. In fact that's the very reason why I'm
>>>> using a Set in the first place.
>>>>
>>>> My question is: Why is the number of entries in the set different when
>>>> I add Arrays vs. adding ASCIIStrings?
>>>>
>>>>
>>>> On Monday, December 14, 2015 at 10:57:57 PM UTC-8, [email protected]
>>>> wrote:
>>>>>
>>>>> I think your problem is that Sets cannot contain duplicate entries, so
>>>>> if Santa ever passes the same point twice it won't be added.
>>>>>
>>>>> Cheers
>>>>> Lex
>>>>>
>>>>> On Tuesday, December 15, 2015 at 4:23:19 PM UTC+10, Jan Strube wrote:
>>>>>>
>>>>>> I'm trying to learn a bit more Julia by solving the puzzles over on
>>>>>> http://adventofcode.com
>>>>>> On day 3, the problem is to follow a number of directions and figure
>>>>>> out how many new places you end up.
>>>>>> http://adventofcode.com/day/3
>>>>>>
>>>>>> I thought I can solve this simply by defining a set of [x y]
>>>>>> positions, each time adding a new grid position to the set, so I'd end
>>>>>> up
>>>>>> with a Set{ Array{Int64,2}} of the right length.
>>>>>> However, this doesn't work as expected. I get the wrong number (it's
>>>>>> too low).
>>>>>>
>>>>>> Wrapping each grid position into a string() call, however, gives me
>>>>>> the right answer.
>>>>>> The explanation is a bit convoluted. To avoid spoilers I've put the
>>>>>> code up at https://gist.github.com/jstrube/3d54e15f7d051b72032b
>>>>>>
>>>>>> I don't quite understand this. Is this expected?
>>>>>>
>>>>>>
