Thoughts about D

[Ola Fosheim Grøstad]

On Thursday, 30 November 2017 at 18:10:01 UTC, Jonathan M Davis 
wrote:
> whereas it would have squeaked by in a smaller object, but it's 
> really a bug to be calling a member function on a null object 
> anyway.

Well, it is a bug, but the member-function may have been written 
with an invariant in mind, so it would then go undetected on a 
small object and continue running with broken invariants (state 
outside the object).

So without such a check there would be reduced value in builds 
with contracts. E.g. there could be a global involved that now 
has a broken invariant. Maybe contracts aren't really a major 
feature anyway, but such gotchas should be listed in the spec at 
least.

> doing that for you and segfaulting. It's just the overly large 
> objects where that's not going to work, and we can add null 
> checks then

I think the objection is that small objects with non-virtual 
member-functions and a path that does not dereference the 
this-pointer will pass incorrectly if this is null.

Assume you  add a non-nullable pointer type.

Then you probably would want to assume that the this pointer is 
never null so that you don't have to test it manually before 
assigning it to a non-nullable pointer variable. Or you risk 
getting null into non-nullable pointers…

But it really depends on how strong you want the type system to 
be.