Help with DMD internals

[Steven Schveighoffer]

On 5/21/18 6:18 PM, Manu wrote:
> On 21 May 2018 at 06:10, Steven Schveighoffer via Digitalmars-d
> <digitalmars-d at puremagic.com> wrote:
>> On 5/20/18 9:49 PM, Manu wrote:
>>>
>>> On 20 May 2018 at 17:14, Walter Bright via Digitalmars-d

>>>> Yes, and only for delete.
>>
>>
>> Why? This doesn't make a lot of sense, since delete is freeing the memory,
>> it shouldn't matter what state the memory is left in. I would argue that
>> should only be done in debug mode, and actually, I wonder if some other kind
>> of sentinel memory pattern should be written instead.
>>
>>>
>>> destroy() also seems to do it.
>>>
>>
>> Yes, because destroy leaves the memory available for reuse. This is
>> intentional.
> 
> It's uninitialised memory though, Wouldn't the same argument you made
> above also apply?

Uninitialized, but allocated and usable. The difference between this and 
delete is that delete is going to unallocate that memory. The next time 
it's allocated, it will be overwritten with an init pattern for the new 
type.

Basically, in D when you have access to memory, it should be in a valid 
state.

This is a valid usage in D:

struct S
{
    this(...) {...}
}

auto s = S(a, b, c);
destroy(s);

// s is now a fully initialized S ready to be constructed
s.__ctor(a, b, c);

-Steve