struct MyStruct; // <- forward declared (opaque type, never defined)

MyStruct*[] arrayOfPointers;

arrayOfPointers ~= null; // appending doesn't work
arrayOfPointers = new MyStruct*[n]; // or just allocating the array doesn't
work either

Complains:
1>code.d(84): Error: struct MyStruct is forward referenced when looking for
'toHash'
1>code.d(84): Error: struct MyStruct is forward referenced when looking for
'opCmp'
1>code.d(84): Error: struct MyStruct is forward referenced when looking for
'toString'
1>code.d(84): Error: struct MyStruct unknown size
1>code.d(84): Error: struct MyStruct no size yet for forward reference
1>code.d(84): Error: struct MyStruct unknown size
1>code.d(84): Error: struct MyStruct no size yet for forward reference

What's the go here?
Why would it need any of that information? It's just a pointer...

Is it even legal D? I though forward declaration was allowed only for "extern(C)" stuff.

On 08/30/2013 10:27 AM, Manu wrote:
> struct MyStruct; // <- forward declared (opaque type, never defined)
>
> MyStruct*[] arrayOfPointers;
>
> arrayOfPointers ~= null; // appending doesn't work
> arrayOfPointers = new MyStruct*[n]; // or just allocating the array doesn't
> work either
>
> Complains:
> 1>code.d(84): Error: struct MyStruct is forward referenced when looking for
> 'toHash'
> 1>code.d(84): Error: struct MyStruct is forward referenced when looking for
> 'opCmp'
> 1>code.d(84): Error: struct MyStruct is forward referenced when looking for
> 'toString'
> 1>code.d(84): Error: struct MyStruct unknown size
> 1>code.d(84): Error: struct MyStruct no size yet for forward reference
> 1>code.d(84): Error: struct MyStruct unknown size
> 1>code.d(84): Error: struct MyStruct no size yet for forward reference
>
> What's the go here?
> Why would it need any of that information? It's just a pointer...
>

The effect on Variant:

  http://d.puremagic.com/issues/show_bug.cgi?id=10766

Ali

So should I extern(C) the forward declaration?


On 31 August 2013 03:45, Dicebot <public@dicebot.lv> wrote:

> Is it even legal D? I though forward declaration was allowed only for
> "extern(C)" stuff.
>

Am Sat, 31 Aug 2013 04:09:10 +1000
schrieb Manu <turkeyman@gmail.com>:

> So should I extern(C) the forward declaration?

Sometimes
---
struct MyStruct {}
---
is used as a workaround, but that may have other issues.

On 8/30/13, Johannes Pfau <nospam@example.com> wrote:
> Am Sat, 31 Aug 2013 04:09:10 +1000
> schrieb Manu <turkeyman@gmail.com>:
>
>> So should I extern(C) the forward declaration?
>
> Sometimes
> ---
> struct MyStruct {}
> ---

Yeah opaque structs have their bugs, I currently use this workaround in dlibgit:

struct MyStruct
{
    @disable this();
    @disable this(this);
}

This should be close to an opaque type, although .sizeof might still work, so it's not 100% opaque.

On Friday, 30 August 2013 at 17:28:12 UTC, Manu wrote:
> struct MyStruct; // <- forward declared (opaque type, never defined)
>
> MyStruct*[] arrayOfPointers;
>
> arrayOfPointers ~= null; // appending doesn't work
> arrayOfPointers = new MyStruct*[n]; // or just allocating the array doesn't
> work either
>
> Complains:
> 1>code.d(84): Error: struct MyStruct is forward referenced when looking for
> 'toHash'
> 1>code.d(84): Error: struct MyStruct is forward referenced when looking for
> 'opCmp'
> 1>code.d(84): Error: struct MyStruct is forward referenced when looking for
> 'toString'
> 1>code.d(84): Error: struct MyStruct unknown size
> 1>code.d(84): Error: struct MyStruct no size yet for forward reference
> 1>code.d(84): Error: struct MyStruct unknown size
> 1>code.d(84): Error: struct MyStruct no size yet for forward reference
>
> What's the go here?
> Why would it need any of that information? It's just a pointer...

http://d.puremagic.com/issues/show_bug.cgi?id=10451

A couple of other forward-ref bugs relating to opaque structs have been recently fixed in git master. If I knew where to look or what to do, I'd fix this one myself. It's an ongoing source of bug reports for Derelict and is bugging the hell out of me.

On Friday, 30 August 2013 at 17:45:14 UTC, Dicebot wrote:
> Is it even legal D? I though forward declaration was allowed only for "extern(C)" stuff.

My understanding of extern(C) is that it just affects the calling convention (and, I assume, name mangling) of functions/function pts and has no impact on types. I haven't seen anything in the documentation to tell me otherwise.

On 31 August 2013 04:59, Johannes Pfau <nospam@example.com> wrote:

> Am Sat, 31 Aug 2013 04:09:10 +1000
> schrieb Manu <turkeyman@gmail.com>:
>
> > So should I extern(C) the forward declaration?
>
> Sometimes
> ---
> struct MyStruct {}
> ---
> is used as a workaround, but that may have other issues.
>

Yeah, that's no good. That certainly opens up more problems.
The point is that it is an undefined struct, and it can only be used to
type a pointer. It's pretty much impossible to extern to a lot of C code if
this doesn't work properly.