Of course, I know how to write the valid code.
But in the interactive environment, if someone accidentally defines the
promote_rule in the non-base way, he will find himself in an
incomprehensible situation.
On Wednesday, August 26, 2015 at 4:15:59 PM UTC+2, Luthaf wrote:
>
> By doing
>
> promote_rule() = 1
>
> And then
>
> Base.promote_rule{T}(::Type{A{T}},::Type{C{T}}) = C{T}
>
> You are defining two different functions. Only the second one is used by
> the promotion system.
>
> The valid code is
>
> abstract B
> type A<:B
> end
>
> type C<:B
> end
>
> Base.promote_rule(::Type{A},::Type{ C}) = C
>
> @assert promote_type(A,C) == C
>
> Sisyphuss a écrit :
>
> In other words, it "won't fix"?
>
> On Wednesday, August 26, 2015 at 6:41:36 AM UTC+2, Stefan Karpinski wrote:
>
> Don't do the first non-base definition.
>
> On Wed, Aug 26, 2015 at 12:27 AM, Sisyphuss <[email protected]> wrote:
>
> This modification works, but it fails sometimes:
>
> abstract B{T}
>
> type A{T}<:B{T}
> end
>
> type C{T}<:B{T}
> end
>
> promote_rule() = 1
> promote_rule()
> @assert promote_type(A{Real},C{Real}) == B{Real}
>
> Base.promote_rule{T}(::Type{A{ T}},::Type{C{T}}) = C{T}
> @assert promote_type(A{Real},C{Real}) == B{Real}
> @assert promote_type(A{Int},C{Int}) == C{Int}
>
> The behavior of `promote_rule` for the abstract parametric type is
> disrupted by the earlier weird non-Base `promote_rule`. (Environment:
> JuliaBox)
>
> By the way, why I can define `promote_rule`, but when I try to define
> `promote_type`, it raises an error?
>
>
>
>
> On Wednesday, August 26, 2015 at 5:25:50 AM UTC+2, Tim Holy wrote:
>
> Add `Base.` in front of `promote_rule`.
>
> --Tim
>
> On Tuesday, August 25, 2015 08:23:40 PM Sisyphuss wrote:
> > abstract B
> >
> > type A<:B
> > end
> >
> > type C<:B
> > end
> >
> > promote_rule(::Type{A},::Type{ C}) = C
> >
> > @assert promote_type(A,C) == B
> >
> > Whether I define the promotion_rule or not, the promote_type is always
> B.
>
>
>
