`restricted` member variables

[Paul Backus]

On Thursday, 23 June 2022 at 00:20:20 UTC, forkit wrote:
> private(this) enables data hiding *within* a module.
>
> you now have the tool needed to define an abstract data type 
> *within* a module.
[...]
> I fail to see the downside (providing the syntax fits in well 
> with the rest of the language, and doesn't stand out like a 
> sore thumb).
>
> once it's in, people will use it, or not, and all this fuss 
> will be long forgotten....

The downside, as with every new language feature, is the cost of 
implementation and maintenance, plus the opportunity cost of 
adding new features instead of working on polishing existing ones.

I freely acknowledge that private(this) has non-zero upside. It 
makes the language more expressive. That, by itself, is not 
enough to justify the addition of a new language feature.

In order for private(this) to be added to D, somebody must 
convince Walter and Atila that the expected upside of it is large 
enough to outweigh the downside inherent to adding *any* new 
language feature.

This is why people are asking for concrete examples, and are not 
satisfied with theoretical justifications alone. They don't just 
want to hear that private(this) *could* be useful; they want to 
be convinced that it *will* be useful, in practice.