Hi Yichao
I get that - I was just curious why (and I guess there's likely a very good
reason for it). My intuition would be that a non-GCed interned string type
could be represented by a bitstype (i.e. a pointer or index to the string
table). So I was surprised that Symbol is an object reference and wanted to
understand this a bit better.
Cheers,
Oliver
On Wednesday, August 17, 2016 at 3:35:41 PM UTC+2, Yichao Yu wrote:
>
>
> > PS: Yes, symbols in Julia should be bitstypes.
>
> No, it's a object reference and isn't a `isbits()` type.
>
>
>>
>> On Wed, Aug 17, 2016 at 8:26 AM, Cedric St-Jean <cedric...@gmail.com
>> <javascript:>> wrote:
>>
>>> Good points.
>>>
>>> Given that symbols have a name which is a string, I don't see how they
>>> could be a bits-type unless they just became numbers to index into a global
>>> array somewhere...... i.e. a pointer. Stack-allocating non-bits-type
>>> immutables is on the roadmap to 1.0, so that should solve your problems.
>>>
>>> Maybe you can solve the CategorizedPoint problem by using an @enum.
>>>
>>> On Wed, Aug 17, 2016 at 6:48 AM, Oliver Schulz <oliver...@tu-dortmund.de
>>> <javascript:>> wrote:
>>>
>>>> Hello Andreas,
>>>>
>>>> consider iterating over a Dict{Symbol,Int64}:
>>>>
>>>> d = Dict(:foo => 42, :bar => 77)
>>>> for x in d println("$(typeof(x)), $(isbits(x))") end
>>>>
>>>>
>>>> During iteration, a lot of stack allocated "Pair{Symbol,Int64}" objects
>>>> are created. That is very bad for performance.
>>>>
>>>> immutable CategorizedPoint
>>>> x::Float64
>>>> y::Float64
>>>> category::Symbol
>>>> end
>>>>
>>>>
>>>> Also, consider a (hypothetical) data type for categorized points (with
>>>> a finite number of categories - but extensible, so that Symbol is a better
>>>> fit than using an enum):
>>>>
>>>> immutable CategorizedPoint
>>>> x::Float64
>>>> y::Float64
>>>> category::Symbol
>>>> end
>>>>
>>>> I would definitely want this to be a bits-type, and not have every
>>>> instance heap-allocated.
>>>>
>>>>
>>>> Cheers,
>>>>
>>>> Oliver
>>>>
>>>>
>>>> On Wednesday, August 17, 2016 at 11:44:13 AM UTC+2, Andreas Lobinger
>>>> wrote:
>>>>>
>>>>> Hello colleague,
>>>>>
>>>>> On Wednesday, August 17, 2016 at 11:12:51 AM UTC+2, Oliver Schulz
>>>>> wrote:
>>>>>>
>>>>>> Sure - I was assuming that as Symbol (as an interned string) is
>>>>>> basically just a pointer. So comparisons are O(1), etc. What I'd like to
>>>>>> understand is, why can't it be a bitstype? Currently, it's not, so
>>>>>> Symbol
>>>>>> cannot be used in a lightweight (i.e. stack-allocated) immutable type. I
>>>>>> assume there's a good reason for it, I just want to understand why.
>>>>>>
>>>>>
>>>>> Could you make an example how you would like to use Symbol in
>>>>> lightweight types?
>>>>>
>>>>>
>>>
>>
>>
>> --
>> Erik Schnetter <schn...@gmail.com <javascript:>>
>> http://www.perimeterinstitute.ca/personal/eschnetter/
>>
>
>
