Leaving a pointer to it on the stack

[Andre Pany]

On Thursday, 13 August 2020 at 20:11:50 UTC, Steven Schveighoffer 
wrote:
> On 8/13/20 4:04 PM, Andre Pany wrote:
>> Hi,
>> 
>> in the specification 
>> https://dlang.org/spec/interfaceToC.html#storage_allocation 
>> there is this paragraph:
>> "Leaving a pointer to it on the stack (as a parameter or 
>> automatic variable), as the garbage collector will scan the 
>> stack."
>> 
>> I have some trouble to understand what does this mean. Given 
>> this example:
>> 
>> ```
>> import std;
>> 
>> void main()
>> {
>>      int* i;
>>      sample(&i);
>>      writeln(*i);
>> }
>> 
>> extern(C) export void sample(int** i)
>> {
>>      *i = new int();
>>      **i = 42;
>> }
>> ```
>> 
>> Int variable is created on the heap. How do I leave a pointer 
>> on the stack?
>> (In the real coding, sample function will be called from 
>> Delphi)
>> 
>
> The garbage collector scans all of the stack as if it were an 
> array of pointers. So if you have a pointer to it anywhere on 
> the stack, it won't be collected.
>
> However, it only scans threads that the runtime knows about.
>
> -Steve

If I understand it right, this paragraph doesn't help in my real 
scenario where sample (Dll) is called from a delphi executable.

It is another runtime (delphi). But on the other side, as D GC 
only runs if something new should be allocated on D side, I can 
safely assume that the Delphi caller can access the heap 
variables? Of course as long as it doesn't store the references 
and use it later...

Kind regards
Andre