alias this of non-public member

[Daniel Kozak via Digitalmars-d-learn]

On Tue, 07 Apr 2015 16:40:29 +0000
via Digitalmars-d-learn <digitalmars-d-learn at puremagic.com> wrote:

> Hi!
> 
> Excuse me if this is obvious, but I can't recall coming across 
> anything similar and a quick search returns nothing relevant:
> 
> struct Foo {
> }
> 
> struct FooWrapper {
>    alias x_ this;
>    private Foo* x_; // doesn't work, as x_ is private
> }
> 
> Basically, I want x_ to never be visible, except through the 
> "alias this" mechanism, at which point it should instead be seen 
> as public.
> 
> Assuming something like this is not already possible in a clean 
> way, I would like to suggest a tiny(I think) addition to the 
> language:
> 
> struct FooWrapper {
>    public alias x_ this; // overrides the visibility through the 
> alias;
>    private Foo* x_;
> }
> 
> 
> While I think this would be useful for the language, the reason I 
> want such a wrapper, is because I want to give opIndex, toString, 
> to a pointer, or, in fact just value semantics, while keeping the 
> rest of the interface through the pointer.
> 
> I thought about using a class instead of a struct pointer, but I 
> am not sure about the memory layout for classes, nor about the 
> efficiency of overriding Object's methods, so I didn't want to 
> risk making it any less efficient. If someone could shed some 
> light about D's class memory layout and general performance 
> differences to a simple struct (or a C++ class for that matter), 
> that would also be great. In general, more information about 
> these sort of things would be great for us also-C++ programmers. 
> :)

Works for me:

struct M
{
	void callMe() {
		writeln("Ring...");
	}
}

struct S
{
	alias m this;
	private M m;
}

void main(string[] args)
{
	S s;
	s.callMe();
}