Issue 7965 - Invalid outer function scope pointer in some cases

[Timon Gehr]

On 06/17/2012 01:45 AM, Era Scarecrow wrote:
> On Saturday, 16 June 2012 at 22:13:44 UTC, Timon Gehr wrote:
>> On 06/16/2012 11:19 PM, Era Scarecrow wrote:
>>> On Saturday, 16 June 2012 at 20:16:52 UTC, Denis Shelomovskij wrote:
>>>> Just want to mention again that Issue 7965 is a really nasty
>>>> wrong-code bug that is difficult to find unless you know about it.
>>>>
>>>> I face this Issue in almost every my D program with non-trivial
>>>> std.algorithm usage and I suppose I'm not alone.
>>>>
>>>> If there is no plans to fix it in near future this _must_ be
>>>> mentioned in std.algorithm Page and in other places in docs because
>>>> it's really possible to avoid it every time you use std.algorithm.
>>>>
>>>> It's not a joke! Such things must be mentioned in docs or D is
>>>> unusable for non-experienced D developers.
>>>>
>>>> http://d.puremagic.com/issues/show_bug.cgi?id=7965
>>>
>>> Looks to me like a frame pointer bug for the delegate (Or lack of
>>> it?)...
>>>
>>> Based on the setup, it should also be illegal to pass the struct
>>> outside of the scope it's in due to the delegate in the struct
>>> (Unless the variable(s) in question are static).
>>
>> Passing the struct outside of the scope it is in must be legal and
>> create a heap frame if it references any of the stack variables.
>>
>> What delegates are you talking about?
>
>   I had the impression that a function referencing the outer frame
> automatically was a delegate; Maybe I just messed up on the terms..
>
> void func(){
>   int x;
>   void y(){x++;};
>
> //equal to??
>   auto y = delegate void(){x++;};
> }

I see. What actually happens looks more like this:

struct StackContext{
     int x;
}
StackContext x;
static void y(StackContext* context){ context.x++; }

No delegate is created until the address of the nested function is
taken. If such a delegate is suspected to escape the frame, the
StackContext is allocated on the heap instead.