This Package provides the Optional{T} type, this type is a simple wrapper
around Union{T, Missing} at least semantically.
In Julia 0.7 and above the Union{T, Missing} type makes it quite convenient to
use fields with optional values. The Missings package tries to backport this
feature to 0.6, unfortunately v0.6 is not very efficient in using Union fields.
In the interim Optional provides a somewhat more efficient way for packages
which need to support both v0.6 and newer. After dropping support for v0.6 and
older, Optional{T} can simply be replaced with Union{T, Missing} (hopefully)
without further changes.
using Optionals
struct Foo
x::Optional{Int}
end
Construction without a value: Foo(missing)
Construction with a value: Foo(42)
Test if field x has a value: ismissing(foo.x)
Get value or replace missing with default: coalesce(foo.x, 42)
Convert an Optional{T} to a Union{T, Missing}: coalesce(foo.x)