But what if I want to restrict the number of a array I use?
if the type is like
type particle
pos
end
and I want to restrict the pos's type to be an Array but the dimension
should be 1,but do not restrict the Type of the Array
or is there any other type can act like a vector but not the Array type?
在 2015年10月15日星期四 UTC+8下午9:06:32，Yichao Yu写道：
>
> On Thu, Oct 15, 2015 at 8:53 AM, Roger Luo <rogerl...@gmail.com
> <javascript:>> wrote:
> > I just start to write the program so I may not have any code to post.
> > I want to define a position of a particle like
> >
> > type particle{T}
> > pos::T
> > end
> >
> > but I hope the type of pos can be limited rather than the supertype any
> >
> > 2015-10-15 20:51 GMT+08:00 Roger Luo <rogerl...@gmail.com <javascript:>>:
>
> >>
> >> It's like what if I want to define a 3-dimension linear space R^3 as an
> >> abstract type and the Array{Float,3} is a subtype-like type of the
> abstract
> >> type 3-dimension linear space?
> >>
> >> I want a linear space as abstract type and some subtypes that can do
> the
> >> linear algebra.
>
> You can define your abstract type (e.g. R^3 Vector) and also define
> your custom concrete type (e.g. R^3 Vector for Float64) that is a
> subtype of it. You cannot change an existing type (like
> Array{Float64,3}) to be a subtype of any abstract type you define.
> (Also note that Float is not a type and Array{Float64,3} is a
> 3-dimensional array and is not a vector in R^3).
>
> To restrict a type parameter to your type, simply use,
>
> type partical{T<:R3Vector}
> pos::T
> end
>
> >>
> >> 2015-09-25 20:36 GMT+08:00 Yichao Yu <yyc...@gmail.com <javascript:>>:
> >>>
> >>> I have some trouble understand your question.
> >>>
> >>> On Fri, Sep 25, 2015 at 8:22 AM, Roger Luo <rogerl...@gmail.com
> <javascript:>>
> >>> wrote:
> >>> > Thanks,I've read about the arrays,but just don't know how to define
> >>> > some
> >>> > existed type.
> >>>
> >>> You cannot redefine a type. Or do you mean how are certain existed
> >>> types implemented? For that you can just check out the source code.
> >>>
> >>> > though a type may be defined as:
> >>> > type a{T<:Integer}<:Real
> >>> > xxx
> >>> > end
> >>> >
> >>> > but that's will work in my function.I tried to pass different types
> >>> > into a
> >>> > function, so I asked this question.
> >>> > still do not understand why can define a existed type become a
> subtype
> >>> > of
> >>> > some other type?
> >>>
> >>> You cannot change the type inheritance of an existing type, period. As
> >>> Mauro pointed out, you are probably looking for something else. It
> >>> would be better if you can post the original problem you are trying to
> >>> solve.
> >>>
> >>> >
> >>> > 2015-09-25 15:11 GMT+08:00 Mauro <maur...@runbox.com <javascript:>>:
>
> >>> >>
> >>> >> Julia's parametric types are invariant (except tuples). To figure
> out
> >>> >> what that means have a read through
> >>> >>
> >>> >>
> >>> >>
> http://docs.julialang.org/en/release-0.4/manual/types/#parametric-composite-types
>
> >>> >>
> >>> >> > How to make Array{BigFloat,1}<:Array{Real,1}?
> >>> >>
> >>> >> This is always false (that is invariance). But presumably you want
> a
> >>> >> method which takes any Array with eltype<:Real, try something like:
> >>> >>
> >>> >> julia> f{T<:Real}(ar::Array{T,1}) = typeof(ar)
> >>> >> f (generic function with 1 method)
> >>> >>
> >>> >> julia> f(Array(BigFloat, 2))
> >>> >> Array{BigFloat,1}
> >>> >
> >>> >
> >>
> >>
> >
>
