OK, I think I got it:
decomplexify{T}(::Type{Complex{T}}) = T
type var2{T,S}
sum::S
sumsqr::T
nobjs::Int64
var2() = new(0,0,0)
end
(::Type{var2{T}}){T}() = var2{T,decomplexify((T))}() << magic?
var2() = var2{Complex{Float64},Float64}() << default
This seems to work
Problem is I have no idea what this line marked "magic" means.
Isaiah Norton wrote:
> See https://github.com/JuliaLang/julia/issues/18466#issuecomment-246713799
>
> On Wed, Sep 14, 2016 at 6:13 PM, Dan
> <getz...@gmail.com> wrote:
>
>> Maybe the following is the form you are looking for:
>>
>> julia> decomplexify{T}(::Type{Complex{T}}) = T
>> decomplexify (generic function with 1 method)
>>
>>
>> julia> type bar{S,T}
>> sum::S
>> sumsqr::T
>> function bar(s,ss)
>> if typeof(ss) != decomplexify(typeof(s))
>> error("Yaiks")
>> end
>> new(s,ss)
>> end
>> end
>>
>>
>> julia> bar{Complex{Float64},Float64}(1.5+2.0im,1.0)
>> bar{Complex{Float64},Float64}(1.5 + 2.0im,1.0)
>>
>>
>> julia> bar{S,T}(x::S,y::T) = bar{S,T}(x,y)
>> bar{S,T}
>>
>>
>> julia> bar(1.5+2.0im,1.0)
>> bar{Complex{Float64},Float64}(1.5 + 2.0im,1.0)
>>
>>
>> The outer constructor is necessary to get the last line working. The
>> inner constructor basically maintains the constraint between S and T of:
>> T == Complex{S}.
>>
>> On Wednesday, September 14, 2016 at 3:38:53 PM UTC-4, Neal Becker wrote:
>>>
>>> Evan Fields wrote:
>>>
>>> > How about something like the following?
>>> >
>>> > type CT{T}
>>> > ctsum::Complex{T}
>>> > ctsumsq::T
>>> > end
>>> >
>>>
>>> I'm aware that it's easier to make the type parameter the scalar type,
>>> allowing writing as you show, but as a learning exercise I'd like to
>>> know how Julia would go the other way.
>>>
>>> In c++ this would be done with template metaprogramming, but as Julia
>>> claims
>>> to have types as 1st class objects, I thought there should be some
>>> elegant
>>> way to do this.
>>>
>>> That is, given T is Complex{U}, I need the type U so I can write
>>> ctsumsq::U
>>>
>>>
