No, you can't change the type of an object.
You can however define types with fields that aren't constrained to be of a
concrete type: while this is worse for performance, it is occasionally
useful, e.g.
type A
a::Union(Void, Int)
end
A(nothing).a = 1
On Saturday, 6 June 2015 23:49:53 UTC+1, andrew cooke wrote:
>
>
> Is there any way to switch the "visible" type - the thing that is
> dispatched on - at runtime?
>
> For example, you might think that a Union() could do this, but the
> "visible" type is either always be the Union, and not either of the
> subtypes, or doesn't allow the value to be changed.
>
> julia> type A{T<:Union(Void,Int)} a::T end
>
> julia> A(1)
> A{Int64}(1)
>
> julia> A(nothing)
> A{Void}(nothing)
>
> julia> A(nothing).a = 1
> ERROR: ...
>
> julia> A{Union(Void,Int)}(nothing).a = 1
> 1
>
> Not sure if those examples make things clear, but when the type of A is
> explicitly A{Void} then the contents cannot be changed to an Int. And if
> the type is explicitly A{Union(...)} then the value can be changed, but the
> "visible" type remains the Union and cannot be dispatched on.
>
> Thanks,
> Andrew
>
>
>
>
