How to create friends of a class at compile time?

[Tejas]

On Thursday, 15 July 2021 at 17:30:05 UTC, jfondren wrote:
> On Thursday, 15 July 2021 at 17:21:45 UTC, Tejas wrote:
>> I can do it like this in C++:
>> ```
>> template<class abc>
>> class def
>> {
>>     friend typename abc;
>> }
>> ```
>>
>> I am just hopelessly confused on how to achieve the same in D.
>
> Uncharitably: D is a friendless language. Charitably: D is so 
> much more friendly that instead of a short explicit list of 
> friends, D has a large implicit list of friends: everything 
> else in a module.
>
> That's why this works:
>
> ```d
> class Secret {
>     private int id;
> }
>
> void main() {
>     import std.stdio : writeln;
>
>     auto s = new Secret;
>     writeln("visible to me: ", s.id);
> }
> ```
>
> But this doesn't:
>
> ```d
> void main() {
>     import std.stdio : writeln;
>     import secret : Secret;
>
>     auto s = new Secret;
>     writeln("visible to me: ", s.id);
> }
> ```
>
> Error: no property `id` for type `secret.Secret`

I'm sorry, I should've explicitly mentioned I'm interested in 
learning how to do friend injection in D.

I know that access specifiers operate at module scope,  seen a 
few posts about that here already.
Thank you for answering though.