Rust Options in Julia

option.jl

struct Some{T}
    val::T
    function Some{T}(val::T) where {T}
        isnothing(val) && error("Cannot have some of nothing")
        return new{T}(val)
    end
end
Some(val::T) where {T} = Some{T}(val)

struct Option{T}
    val::Union{Some{T}, Nothing}
end
Option(arg::T) where {T} = Option{T}(val)

unwrap(some::Some{T}) where {T} = some.val
is_none(opt::Option{T}) where {T} = isnothing(opt.val)
is_some(opt::Option{T}) where {T} = !is_none(opt)