bug: vscode extension warns about possible nulls where it's not possible
Why I get this yellow wave line under the comparsion? I thought this was already fixed long ago (though that might have been in the compiler, not the vsc extension)
> It seems that the actual problem has nothing to do with local vs non-local variables, but with the presence of any kind of explicit scope specifier ($, self, class name, module name).
Then again I still see a variant of this problem with a static member variable (no self prefix), so I guess this is a bit more complex than I assumed (or there are in fact multiple problems)
Or I could be 100% wrong and it's actually a bug, as it seems type narrowing of non-locals works in *some* cases.
e.g.
It seems that the actual problem has nothing to do with local vs non-local variables, but with the presence of any kind of explicit scope specifier ($, self, class name, module name).
I would argue that this is a more of a limitation / missing feature than a bug (as in code that's supposed to work one way but actually works a different way). (Yes it's a bug from our pov ofc).
The type checker apparently just doesn't have the ability to narrow / infer the type of anything other than a local variable. And I think it's possible in theory (obviously typescript is able to do so)
As this example shows, typescript:
- can narrow the type of a non-local variable (good)
- but it doesn't notice that a non-local variable's type can be changed by other code after narrowing (bad). In this sense, Monkey C is actually safer than TypeScript
Type narrowing doesn't work for non-local variables. If you rewrite the code with intermediate local variables, then it works as expected.
I understand the limitation here - it's similar to why types can only be inferred for local variables: because the compiler can't always know that you aren't assigning some value to a global or member variable that reset its idea of what the type is.
But I would argue that the compiler can and should be smarter in cases like the examples you have given.
