Re: no size yet for forward reference for nested structures

[Ali Çehreli via Digitalmars-d]

On 01/14/2015 02:53 AM, ketmar via Digitalmars-d wrote:
> On Wed, 14 Jan 2015 10:41:07 +0000
> qqiang via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
>
>> template PowerHeap(T) {
>>       import std.container : SList;
>>
>>       private alias PowerForest = SList!PowerNode;
>>
>>       private final class PowerNode {
>>           private {
>>               T payload_;
>>               uint rank_;
>>               PowerForest children_;
>>           }
>>       }
>>
>>       final class PowerHeap {
>>           private {
>>               PowerNode top_;
>>               PowerForest forest_;
>>               uint size_;
>>           }
>>       }
>> }
>>
>> unittest {
>>       PowerHeap!int h;
>> }
> there is a circular dependency in your data structures. you're defining
> `PowerNode` in the terms of... `PowerNode`. this won't work.
>
> your `PowerForest` definition depends of complete `PowerNode`
> definition, but `PowerNode` definition depends of complete
> `PowerForest` definition.
>
> don't do that.
>

Reduced:

import std.container;

class Node
{
    SList!Node children;
}

void main()
{}

Error: class deneme.Node no size yet for forward reference

I wonder why an SList of a reference type requires the size of the 
elements? The following compiles but is that a pointer to a class 
variable or a class object? How can we even use the 'children' member?

    SList!(Node*) children;

Ali