NoUseForAName:

> Thanks, that is what I was looking for.

Why do you need a public pointer type but private struct type?

Bye,
bearophile

On Tuesday, 8 July 2014 at 11:42:54 UTC, NoUseForAName wrote:
> On Tuesday, 8 July 2014 at 11:16:52 UTC, Marc Schütz wrote:
>> Your example above doesn't work, because it would be interpreted as a redefinition of the struct. Instead, you can use a public alias to a private type:
>>
>> // my_module.d:
>>
>> private struct MyStructImpl {
>>    int x;
>> }
>>
>> public alias MyStructPtr = MyStructImpl*;
>>
>> void doSomething(MyStructPtr foo) {
>>    ...
>> }
>>
>> // my_main_program.d:
>>
>> MyStructPtr bar;    // OK
>> MyStructImpl foo;   // Error: my_module.MyStructImpl is private
>
> Thanks, that is what I was looking for.

Addendum: You also need to protect the members of MyStructImpl, like so:

private struct MyStructImpl {
private:  // or `package:`
    int x;
}

Otherwise, they would still be accessible via dereferencing. (Don't worry, you _can_ access private members inside the module the struct is declared in, as access protection in D only applies across module boundaries.)

On Tuesday, 8 July 2014 at 11:55:01 UTC, bearophile wrote:
> NoUseForAName:
>
>> Thanks, that is what I was looking for.
>
> Why do you need a public pointer type but private struct type?

As the OP wrote:
> In C my favorite way of achieving encapsulation is to use incomplete types.

(Also known as PIMPL.)

In C, it's the only type-safe way to get encapsulation, AFAIK. In languages with access protection, it's probably not as useful, but I'm sure it has its applications...

On Tuesday, 8 July 2014 at 12:04:40 UTC, Marc Schütz wrote:
> Addendum: You also need to protect the members of MyStructImpl, like so:
>
> private struct MyStructImpl {
> private:  // or `package:`
>     int x;
> }
>
> Otherwise, they would still be accessible via dereferencing.

Thanks again.

On 07/08/2014 03:35 AM, bearophile wrote:

> Ali Çehreli:
>
>> 1) Put the opaque type and its functions into a .di file:
>
> [...]
>
> It seems your answer has scared NoUseForAName off. Next times we need to
> be more careful, and suggest a D-idiomatic solution instead.
>
> Bye,
> bearophile

I should have first asked what the need was.

Ali