Well, this is one of the ugly things and actually not new:
Bar{Float64}(1, 8)
should do the trick.
The other doesn't work, because you can't construct Bar with more than two
values.
This happens because you did overwrite the default constructor, allowing to
construct bar only with x and y.
T can't be inferred from this (as it's not used in the signature of your
constructor) so you need to supply it.
This issue might
help: https://github.com/JuliaLang/julia/issues/10146#issuecomment-74092508
Am Dienstag, 17. Februar 2015 19:59:00 UTC+1 schrieb Ismael VC:
>
> Why can't I create an instance of this `Bar` type with the following
> enforced invariants?
>
> julia> versioninfo()
> Julia Version 0.4.0-dev+3353
> Commit 0179028* (2015-02-14 17:08 UTC)
> Platform Info:
> System: Windows (x86_64-w64-mingw32)
> CPU: Intel(R) Core(TM) i3 CPU M 350 @ 2.27GHz
> WORD_SIZE: 64
> BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Nehalem)
> LAPACK: libopenblas
> LIBM: libopenlibm
> LLVM: libLLVM-3.3
>
> julia> abstract Foo
>
> julia> type Bar{T<:Number} <: Foo
> value::Nullable{Complex{T}}
> x::Int
> y::Int
>
> function Bar(x::Int, y::Int)
> x < 0 || y < 0 && error()
> x < y ? new(Nullable{Complex{T}}(), x, y) : error()
> end
> end
>
> julia> Bar{T<:Number}(value::T, x::Int, y::Int) =
> Bar(Nullable(complex(value)), x, y)
> Bar{T<:Number}
>
> julia> methods(Bar)
> 2-element Array{Any,1}:
> call{T<:Number}(::Type{Bar{T<:Number}},value::T<:Number,x::Int64,y::Int64)
> at none:1
> call{T}(::Type{T},args...) at base.jl:36
>
> julia> Bar(1, 8)
> ERROR: MethodError: `convert` has no method matching
> convert(::Type{Bar{T<:Number}}, ::Int64, ::Int64)
> This may have arisen from a call to the constructor Bar{T<:Number}(...),
> since type constructors fall back to convert methods.
> Closest candidates are:
> convert{T}(::Type{T}, ::T)
>
> in call at base.jl:36
>
> julia> Bar(5.7, 1, 8)
> ERROR: MethodError: `convert` has no method matching
> convert(::Type{Bar{T<:Number}}, ::Nullable{Complex{Float64}}, ::Int64,
> ::Int64)
> This may have arisen from a call to the constructor Bar{T<:Number}(...),
> since type constructors fall back to convert methods.
> Closest candidates are:
> convert{T}(::Type{T}, ::T)
>
> in call at none:1
>
> How could I implement the this type's constructors? I don't understand the
> new `call` constructors! :'(
>
>
