Help with DMD internals

[Steven Schveighoffer]

On 5/22/18 9:48 PM, Manu wrote:
> On 22 May 2018 at 06:44, Steven Schveighoffer via Digitalmars-d
> <digitalmars-d at puremagic.com> wrote:
>> On 5/22/18 1:01 AM, Manu wrote:
>>> Ah! Dangling pointers... that might conservatively retain garbage.
>>> That's a good reason.
>>
>>
>> Well, I was thinking more along the lines of accessing memory that is no
>> longer valid :) A destructor can, for instance, free C malloced memory.
> 
> The memory post-destruction is invalid... nobody will access it.
> Accessing it should be undefined behaviour until such a time as the
> memory is re-constructed with a new instance...
> 

This particular sub-thread was about using destroy on something, not 
freeing the memory. The memory is not invalid.

To clarify, I'm talking about something like this:

struct S
{
   int *foo;
   this(int x) { foo = cast(int*)malloc(int.sizeof); }
   ~this() { free(foo); }
}

auto s = S(1);
destroy(s);
*s.foo = 5; // oops

If s.foo is reset to null, then you get a nice predictable segfault. If 
not, then you get memory corruption. Sure you can just say "undefined 
behavior", but I'd rather the defined behavior.

-Steve