None?

[Udiknedormin]

It seems to me there are two possible solution:

1. provide a wrapper for non-nilable types and translate None for them for this wrapper constructor
2. provide a wrapper for any type specialized for nilable types and translate any None call to it

It seems to me the second one is easier. Unluckily there is no return-type generic overloading in implicit conversions so a type None[T] type rather than const None: NoneType should be used. It would works like this:

var w = "wrap".pyWrap()
w = "value"                # ok, returns PyWrapper("value")
let s: string = w          # ok, returns "value"

var y = @[2,7,1]
y = @[8, 2, 8].pyWrap()    # ok, returns @[8, 2, 8]
y = none(y)                # ok, returns nil
y = none(type(y))
y = None[type(y)]()
y = none(y).pyWrap()       # ok, returns nil

var x = 3
x = 1.pyWrap()             # ok, returns 3
x = none(x).pyWrap()       # runtime-error: "None dereference"
x = pyWrapNone(x)
x = none(x)                # compile-time error: "`int` type is not nilable!"

So in fact, all lhs = None assignments should be translated to lhs = pyWrap(none(lhs)). Of course they can form a cycle with generic arguments and then some additional type annotation would be needed.

Actually, I have already implemented PyWrapper which works for these examples but I'm not sure if it's the best approach available, especially considering no generic implicit conversions...