Error: 'this' is only defined in non-static member functions, not main

[anonymous via Digitalmars-d-learn]

On Wednesday, 29 July 2015 at 21:33:16 UTC, remi thebault wrote:
> Hello
>
> I have this weird error trying to achieve something simple:

That's far from simple.

Here's a reduction:

----
template wl_container_of(alias member)
{
     size_t get() {return member.offsetof;}
}

struct item { int link; }

void main()
{
     wl_container_of!(item.link).get(); /* Error: 'this' is only 
defined in non-static member functions, not main */
}
----

I'm not sure what's going on here, if this should or shouldn't 
work. The error message isn't exactly good.

Slapping `static` on `get` seems to make it work:
----
     static size_t get() {return member.offsetof;}
----

I guess the compiler thinks that since `item.link` is an instance 
member, it needs a `this`. And then `get` would need a `this` too 
as it's using `item.link` via `member`. When the compiler sees 
that there is no `this`, it errors out.

An explicit `static` forces the compiler to assume no `this`. And 
it would error out if you actually tried to make use of it.

Naively, I'd think the compiler should be able to figure that out 
itself.