I found your proposal
https://groups.google.com/forum/#!searchin/julia-users/vavasis/julia-users/Hq00EyeazJM/HgYgDcnbhs4J
https://groups.google.com/forum/#!searchin/julia-users/vavasis$20const/julia-users/FK_29Dj4eDo/nX5QnhfKc40J
but that is a different feature, having cont `in` argument, while I want
const return types.
Having const in would be nice, but i understand that its implementation
would be more difficult.
On the other hand having a const return valure seems easier to my
(non-expert) eyes
Il giorno martedì 27 ottobre 2015 04:27:44 UTC+1, vav...@uwaterloo.ca ha
scritto:
>
> In 2014 when I first learned about Julia, I also suggested on this
> newsgroup that there should be a 'const' keyword as in C++ to annotate
> function arguments and return variables that are supposed to be read-only.
> Possibly you can find the old thread with google. I received a lot of
> feedback from experienced Julia users and core developers that convinced me
> that this is probably not a good idea. Here are some reasons that I can
> recall from the earlier discussion that adding 'const' to Julia may not be
> a good idea.
>
> (1) The 'const' keyword would make the multiple-dispatch system much more
> confusing because it would entail new rules about how the 'const' keyword
> affects closeness in the type hierarchy.
>
> not a problem for const return value
> (2) You can already get the desired effect in Julia by defining your own
> subtype of DenseArray in which getindex works as usual but setindex! throws
> an error.
>
> this solution is not general, it works only on arrays
> (3) The promise that a routine won't change a 'const' argument could
> easily be defeated by aliasing (i.e., a function is invoked with a const
> argument, but another non-const argument refers to the same piece of data),
> so it may give the user a false sense of security.
>
not a problem for const return value
-- Steve Vavasis
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> On Monday, October 26, 2015 at 10:29:34 PM UTC-4, Carlo Lucibello wrote:
>>
>> It would be nice to annotate the return type of methods with a constant
>> qualifier, in order to have
>> an efficient and safe behaviour at the same time.
>>
>> I mean something like this:
>>
>> type A
>> data::Vector{Int}
>> end
>>
>> # invalid but desiderable julia code
>> const function getdata(a::A)
>> return a.data
>> end
>>
>> a = A(ones(10))
>> data = getdata(a)
>>
>> data[1] = 2 # ERROR
>> a.data[1] = 2 # OK
>>
>>
>
