Safe Navigation Operator “?.” for D2 ?

[deadalnix]

On Friday, 28 February 2014 at 12:28:22 UTC, John Colvin wrote:
> Do you mean:
>
> Chaining operations that can return null (or some other 
> known-to-be-invalid state) is a code-smell.
>

That is the worse.

> That's quite different to saying:
>
> Chaining operations using . is a code-smell.
>
> which is what deadalnix said.
>

Yes. That must not be understood as a hard rule, but something 
that is true most of the time. You want to look up "Law of 
Demeter". The problem when you chain is that you make a lot of 
code dependent on the structure of the project, which makes it 
hard to evolve or maintain the project, as any change in the 
structure will impact more code than it should.

Obviously, this idea may be in tension with other principle, and 
good judgement is always welcome. As a general rule, unless you 
have some really good reason to, avoid chaining.

>
> Either way, a do-this-if-you-can pattern is quite reasonable 
> IMO. However, I do question whether it's common enough to 
> justify syntax sugar.

This pattern exist. That is called the maybe monad. To take 
previous example:
writeln(person ? person.name : "");

Can become
Maybe!Person person;

writeln(person.name.get(""));

If person is a Maybe!Person, the person.name is a Maybe!string 
(assuming name is a string) and the get method will provide a 
default value if nothing is present in the Maybe monad.

That ensure that null is checked consistently and provide what 
you want, a do-this-if-you-can pattern.