Inheriting from nil fails too late

[fendrin]

Parent = nil 

class Some extends Parent
...

This fails when the constructor of "Some" is called.
The error message

attempt to index local '_parent_0' (a nil value)

isn't that helpful before you look into the implementation details of class.

I suggest to let the code that defines the class check for nil parent and write a more useful error message.

[Idyllei]

👍 After delving into some of Perl 6 code, I very strongly agree with @fendrin that this fails too late. I suggest that the translator fail as soon as possible once it encounters a case of inheriting from nil. (Perhaps, if the 'compiler' failing is not desirable, the Lua code that creates the constructor might error if it detects that it will inherit from nil before it can be called.)

[RyanSquared]

With the rest of MoonScript, the only required external dependency when compiling .moon files is MoonScript. Inherited classes must be checked runtime, if at all.

[leafo]

There are currently no runtime checks that throw errors in any moonscript generated code. Should I add dependency on assert or error built in functions? Another option, maybe instead of naming the variable _parent_0 it could be called Some_parent (Some being the name of the class). You would most likely be able to immediately tell what the problem is from the attempt to index nil error at that point

[TangentFoxy]

I vote for naming the variable after the class name, since you don't currently depend on assert/error anywhere else, and it would make generated code easier to read in addition to making the error easier to find.

(Is there anywhere else the generic _something_# naming of variables can come up with a hard-to-find error? I can't think of any off the top of my head, but if there is, it might be worth looking into as well.)