free causes exception

[Steven Schveighoffer via Digitalmars-d-learn]

On 1/26/16 4:23 PM, Igor wrote:
> On Tuesday, 26 January 2016 at 20:17:20 UTC, Steven Schveighoffer wrote:
>> On 1/26/16 9:20 AM, Igor wrote:
>>> I have successfully malloc'ed an object but when I go to free it in the
>>> destructor I get an exception. The destructor simply has
>>>
>>> ~this() // destructor for Foo
>>> {
>>>      core.stdc.stdlib.free(&this);
>>> }
>>>
>>>
>>> auto buffer = core.stdc.stdlib.malloc(__traits(classInstanceSize,
>>> App))[0..__traits(classInstanceSize, App)];
>>> auto app = cast(App)emplace!App(buffer[]);
>>>
>>> I tried to retain a ptr to buffer and free that but still no good. I
>>> also get a depreciation warning that &this is not an lvalue. Hopefully I
>>> don't have to keep a ptr around to this simply to free it and avoid
>>> future issues?
>>>
>>> So how am I suppose to free an object?
>>
>> Don't do it in the destructor.
>>
>> I can only imagine that you are triggering the destructor with
>> destroy? In this case, destroy is calling the destructor, but then
>> tries to zero the memory (which has already been freed).
>>
>> There is a mechanism D supports (but I believe is deprecated) by
>> overriding new and delete. You may want to try that. It's deprecated,
>> but has been for years and years, and I doubt it's going away any time
>> soon.
>>
>> A class shouldn't care how it's allocated or destroyed. That is for
>> the memory manager to worry about.
>
> um? Memory manager? I am doing it manually C++ style so I don't have to
> worry about the god forsaken memory manager. Why is it so difficult? I
> create the object and release it when I need to.

As Mike said, I mean whatever you are using for memory management. The 
class is not responsible for allocating or deallocating itself, just 
initializing itself and deinitializing itself.

So if you use malloc and free, that is your memory manager.

>
> I can replace the destroy(f) with free(inline the code) but I don't see
> why that should matter. The whole point of destructors is to do this
> sort of stuff. That's why they were invented in the first place!?!

It isn't even this way in C++. No destructors deallocate 'this'.

All D destructors should destroy all the members. And generally 
speaking, if you ever plan to use a class with the GC, you should only 
destroy non-GC members. The GC members may already be destroyed.

-Steve