Why does nobody seem to think that `null` is a serious problem in D?

[Neia Neutuladh]

On Tue, 20 Nov 2018 00:30:44 +0000, Jordi Gutiérrez Hermoso wrote:
> On Monday, 19 November 2018 at 21:57:11 UTC, Neia Neutuladh wrote:
> 
>> Programmers coming from nearly any language other than C++ would find
>> it expected and intuitive that declaring a class instance variable
>> leaves it null.
> 
> What do you think about making the syntax slightly more explicit and
> warn or possibly error out if you don't do it that way?

The prevailing idea is that warnings are either non-problems, in which 
case they shouldn't be emitted, or things you really need to fix, in which 
case they should be errors.

Things that are sometimes errors can be left to lint tools.

> Either
> 
>    SomeClass c = null;
> 
> or
> 
>    SomeClass c = new SomeClass();
> 
> and nothing else.

That would work, though it would be mildly tedious.

However, the general philosophy with D is that things should be implicitly 
initialized to a default state equal to the `.init` property of the type. 
That default state can be user-defined with structs, but with other types, 
it is generally an 'empty' state that has well-defined semantics. For 
floating point values, that is NaN. For integers, it's 0. For arrays, it's 
a null array with length 0. For objects and pointers, it's null.

> Nulls/Nones are always a big gap in a language's type system. A common
> alternative is to have some Option/Maybe type like Rust or Haskell or
> D's Variant.

Variant is about storing arbitrary values in the same variable. Nullable 
is the D2 equivalent of Option or Maybe.

> How about making that required to plug the null gap?

That's extremely unlikely to make it into D2 and rather unlikely to make 
it into a putative D3. However, if you feel strongly enough about it, you 
can write a DIP.

I've used Kotlin with its null safety, and I honestly haven't seen 
benefits from it. I have seen some NullPointerExceptions in slightly 
different places and some NullPointerExceptions instead of empty strings in 
log messages, but that's it.