But then the question is why we define specialized versions for Bool rather
than using the methods for Real in number.jl. For all but abs LLVM is smart
enough to optimize the methods for Real to no-ops.
Simon
On Thursday, September 11, 2014 5:27:10 AM UTC-4, Tim Holy wrote:
>
> It's because
>
> julia> super(Bool)
> Integer
>
> julia> super(Integer)
> Real
>
> and you'd expect these to be defined for Integers. If this weren't the
> case
> then
>
> function myalgorithm{T<:Real}(x::AbstractArray{T})
> # do something involving abs
> end
>
> would fail if the user supplied an array of Bools. I could create a
> special
> version of myalgorithm for Array{Bool} that omitted calls to abs, but that
> would be a pain in the neck, and I'd have to worry about every single
> possible
> element type ("does Uint16 have an abs method? let's check"). Since Julia
> compiles a new version of myalgorithm specificially for Array{Bool},
> there's
> also no performance hit (such trivial functions just get inlined out into
> no-
> ops).
>
> --Tim
>
> On Wednesday, September 10, 2014 10:20:42 PM Dan Luu wrote:
> > In bool.jl, there are things like
> >
> > signbit(x::Bool) = false
> > sign(x::Bool) = x
> > abs(x::Bool) = x
> > abs2(x::Bool) = x
> >
> > Are these because Bool is a subtype of something where you'd expect
> > these to be defined, or are these useful in their own right, and if
> > so, when would you use these?
> >
> >
> > Thanks,
> > Dan
>
>
