GC being too eager?

[Paulo Pinto]

On Thursday, 10 April 2014 at 09:31:30 UTC, John Colvin wrote:
> On Thursday, 10 April 2014 at 09:24:51 UTC, Paulo Pinto wrote:
>> In a toy project I am working on with D v2.065, I came to the 
>> following situation:
>>
>> Node path = solver.find (map, start, end);
>> if (path !is null) {
>>    path.writeContents();  <-- Access Violation
>> }
>>
>> Apparently between the test and trying to use the class, the 
>> reference becomes null.
>>
>> Quite strange in a single threaded application.
>>
>> Any idea what might be happening or should I delve into 
>> assembly?
>>
>> --
>> Paulo
>
> Delve delve delve. Is this in an optimised build?

I found out the cause, apparently std.container.Array destroys 
the memory used by reference types as well (e.g. classes).

The small example below reproduces the error.

Apparently the way Array manages the memory on its own 
invalidates the reference pointed by node, as I assume bad == 
node, but its memory is invalid.

import std.stdio;
import std.container;


class Node {
}

Node indentity (Node n)
{
     return n;
}

Node badIndentity (Node n)
{
     Array!Node data;
     data.insert(n);
     return data.front();
}

int  main(string[] args)
{
     auto node = new Node();
     auto n = indentity (node);
     writefln("Hello the address is %s", n);
     auto bad = badIndentity (node);
     writefln("Hello the address is %s", bad);

     return 0;
}