extern(C) and mangling type names

[Mike Parker via Digitalmars-d]

On Wednesday, 15 February 2017 at 10:59:25 UTC, Kagamin wrote:
> On Wednesday, 15 February 2017 at 03:40:32 UTC, Mike Parker 
> wrote:
>> My specific use case is a binding to a C library that makes 
>> use of specific types from X11, Wayland and elsewhere.
>
> If X11.Foo is implicitly convertible to forward reference Foo 
> and forward reference Foo is implicitly convertible to 
> Wayland.Foo, then X11.Foo is implicitly convertible to 
> Wayland.Foo.

Not quite what I meant. I want to use X11 types without forcing 
the user to choose between Tom's X11 bindings and Jerry's. The 
user should be able to use either. Ditto for multiple Wayland 
bindings. So, for example:

version(UseX11) {
     struct Display;
     alias EGLNativeWindowType = Display*;
}
else version(UseWayland) {
     struct wl_display;
     EGLNativeWindowType = wgl_display*;
}

Then when compiling with UseX11, the user can import tom.x11 or 
jerry.x11, whichever he prefers.

It's so tantalizingly close to being possible. My earlier example 
compiles and runs when using type inference:

module ec3;
void main() {
     import ec1, ec2;
     auto f = newFoo(30);
     printFoo(f);
}

My intuition is screaming at me. If this works, then shouldn't it 
also work when I declare the type myself?

And if I add `alias MyFoo = Foo*` to ec1, then the first error, 
the one about conflicts, goes away, but I still get the latter 
two errors related to the function call. Why? I'm still returning 
an ec2.Foo* and assigning it to an ec1.Foo*. An alias is just a 
synonym. The types haven't changed.