Using closure in function scope to make "real" private class members

[forkit]

On Sunday, 5 June 2022 at 04:49:44 UTC, forkit wrote:
>

btw.

here is a simple example, for demonstration purposes only, of the 
change that I'd like to see in D:

It's benefit seems very obvious to me ;-)

First, the invariants of the class are now upheld by the compiler.

Second, those of us who expect invariants to be upheld, can now 
have it.

Third, it's completely optional. Nobody has to change anything 
they currently do. If you don't want it, don't use it.


// ----
module test;

// example: @private is an access specifier, that works just as 
private does,
// except, that @private is encapsulated to the class (or struct).

class ID
{
     import std.string;

     @private:
         string _id;

     public
         void setID(string id)
         {
             assert(isNumeric(id));
             _id = id;
         }
}

unittest
{
     import std.stdio;

     ID id = new ID();

     id.setID("123"); // Fine. The invariant is maintained.
     writeln(id._id);

     id._id = "dsa"; // This would violate the invariant.
                     // The compiler would never allow this with 
@private
     writeln(id._id);
}

// -----