Thread overview
Forward references
Feb 25, 2018
Jiyan
Feb 25, 2018
ketmar
Feb 25, 2018
Jiyan
Jun 10
Elmar
February 25, 2018
Hi,
is there any document or text describing forward references?
It is kinda strange, i implemented a list structure which is kinda like this:

struct list(T)
{
private:

struct node
{
T val;
node* next;
node* prev;
}

node* head;
node* last;
size_t size;

 .....
}

The thing is when i implement following struct:

struct Tre
{
list!Tre a;
}

theoretically it should be constructable. But it gives me out a compiler error about Forward reference. Ok maybe the compiler at this point cant do that but ...

The strange thing is i somehow managed earlier without knowing to do exactly this in a much more complicated struct.
Can somebody enlighten me about this?





February 25, 2018
works for me with 2.076.
February 25, 2018
On 2/25/18 4:25 PM, Jiyan wrote:
> Hi,
> is there any document or text describing forward references?
> It is kinda strange, i implemented a list structure which is kinda like this:
> 
> struct list(T)
> {
> private:
> 
> struct node
> {
> T val;
> node* next;
> node* prev;
> }
> 
> node* head;
> node* last;
> size_t size;
> 
>   .....
> }
> 
> The thing is when i implement following struct:
> 
> struct Tre
> {
> list!Tre a;
> }
> 
> theoretically it should be constructable. But it gives me out a compiler error about Forward reference. Ok maybe the compiler at this point cant do that but ...
> 
> The strange thing is i somehow managed earlier without knowing to do exactly this in a much more complicated struct.
> Can somebody enlighten me about this?

Looks like this was fixed in 2.064.

What version of the compiler are you using?

-Steve
February 25, 2018
On Sunday, 25 February 2018 at 22:20:13 UTC, Steven Schveighoffer wrote:
> On 2/25/18 4:25 PM, Jiyan wrote:
>> [...]
>
> Looks like this was fixed in 2.064.
>
> What version of the compiler are you using?
>
> -Steve

2.077.0

It is really strange, it works now but there still seems to be some strangeness about forward references.

Thanks till now i guess :P
February 25, 2018
On 2/25/18 6:53 PM, Jiyan wrote:
> On Sunday, 25 February 2018 at 22:20:13 UTC, Steven Schveighoffer wrote:
>> On 2/25/18 4:25 PM, Jiyan wrote:
>>> [...]
>>
>> Looks like this was fixed in 2.064.
>>
>> What version of the compiler are you using?
>>
>> -Steve
> 
> 2.077.0
> 
> It is really strange, it works now but there still seems to be some strangeness about forward references.

There are frequently issues with forward references. They are supposed to always work, but it's not always the case.

-Steve
June 10

Hello there,

I got a weird compilation error which was hard to debug (even for just a little program) and I thought, this is quite related to this thread. This is my error message:

***search.d(42,1): Error: class ***.XXX has forward references
***box.d(21,32): Error: template instance *** error instantiating
***.d(16,2):        instantiated from here: ...
...

It was odd, the fix was not obvious and the compiler didn't show me the place of the erroneous forward reference. The problem was a scoped import statement!! I had put the import statement for the Box class into the abstract base class Search, the only place where it is used, but this seems to cause a mess with many errors. The imported Box uses a sub class of Search as parameter type and since Search is extended by its subclasses it creates a circular reference in the subclass. The only way to fix was putting the import outside of the abstract base class (I assume because the import statement literally imports the Box together with the used subclass into Search itself).

The lesson is, you cannot put your import just everywhere.