On Thursday, 28 August 2014 16:48:31 UTC+2, R. Fourquet wrote:
>
> > Sorry, I had some errors in this next bit.
>
> >> myfun(a :: Union(EuclideanPoly, Poly))
>
> > It should have been
> > myfun{T <: Union(EuclideanPoly, Poly)}(a :: T)
>
> The first version is perfectly ok and more idiomatic in this case. You
> said earlier:
>
> > So typically function signatures will look like
> > fnname{T <: Z}(a :: T)
> > where we have:
> > a is a value
> > T is a type
> > Z is a typeclass
>
> Function signatures typically look like this only when T (a type
> variable) is used in the function definition, e.g.
> myfun{T}(::Poly{T}) = T
>
> or to constrain argument types, e.g.
> myfun{T}(a::Poly{T}, b::Poly{T}) = a+b # a and b must be Polys of the same
> type
>
> or to constrain the type variable, e.g.
> myfun{T<:Field}(a::Poly{T}) = 1/coeff(a)[1] # method of myfun working
> only with Polys over fields (and "myfun(a::Poly{<:Field})" is
> envisioned)
>
> Otherwise, "fname(a :: Z)" is the way, even if Z is abstract
> (typeclass). And even then, the concrete type of "a" can be referred
> to via "typeof(a)". And fname will be compiled separately for each
> concrete type it is called on.
>
Thanks very much for pointing that out. I was not aware of this trick!
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