[julia-users] Constructors for types with Nullable fields

[Helge Eichhorn]

Hi,

let's say I have the following type with two Nullable fields:

type WithNulls 
    a::Nullable{Float64} 
    b::Nullable{Float64}
end


I now want the user to be able to create an instance of this type without 
caring about Nullables. For this I use a constructor with keyword arguments.


function WithNulls(;
    a = Nullable{Float64}(),
    b = Nullable{Float64}(),
)
    WithNulls(a, b)
end


This works for Float64 but not for the other leaf types of Real.


# Works
WithNulls(a=3.0)

# Does not work
WithNulls(a=pi)


This can be fixed by adding the following methods to convert:


Base.convert{T<:Real}(::Type{Nullable{T}}, v::T) = Nullable{T}(v)
Base.convert{T<:Real,S<:Real}(::Type{Nullable{T}}, v::S) = Nullable{T}(
convert(T,v))


Finally the question:

Should the above convert methods not be part of Base? I think converting 
between different Nullable{T<:Real} values might be a common use case. Is 
there a more elegant way to do this?