Assert doesn't erase nilable when used in branch tail...

[jcorbin]

Rather it only seems to work when it's in the main branch.

This fails:

class such:
    x = 0

var much = nil

if not much:
    much = such {}
    assert much

much.x++
print(much)

much.x++
print(much)

With foo.lobster(10): error: type such? does not have field: x

But hoisting the assert much works.

This has been a contrived example, reduced down from something like:

• a class with a nil-able resource? field
• where I load it the first time through, something like if not tex: load()
• where there's a def load() method that ends with an assert tex after having loaded from a file
• I ended up just inlining the loader method, and hoisting its guard assertion into main control flow...

[aardappel]

Yeah, there's currently no flow information going out of scopes. If there was, the assert wouldn't even be necessary, since much = such {} already makes it non-nil.

But yeah, this would require interesting logic, since now we need to basically say, both "branches" of the if come to the same conclusion for a certain variable, so that information can be merged. That would be a new kind of construct in the typechecker.

I guess I haven't run into this much, since the nil checking just makes me religiously try to avoid any nils in my code :)