`restricted` member variables

[forkit]

On Thursday, 23 June 2022 at 00:48:13 UTC, Paul Backus wrote:
>
> ..

I disgree. It will mean D can finally be taken seriously.

With private(this), you are not longer constrained to defining a 
type using the D module mechanism.

You can now actually create 'real' user-defined types.

As we already now, in D, a type created using the modular 
mechanism, gets even less suppport than an int type.

By that I mean, I use can use an int type throughout my module, 
and it's invariants will hold. The compiler will make sure of 
this.

The same is not true for user-defined types, because they are 
enabled using the D module mechansim.

That is, they do not own their type, so they cannot declare let 
alone enforce invariants, since module owns them.

Thus any invariants of the user type cannot only be declared and 
enforced by the module, and not the type.

Such types are not user-defined types.

With private(this), D turns into a language that supports 
user-defined types.

That's a big deal, IMO.