Destructor nonsense on dlang.org

[Artur Skawina]

On 05/26/12 13:35, Jacob Carlborg wrote:
> On 2012-05-25 14:05, foobar wrote:
> 
>>> If you have a pointer to a struct you don't know how it was created.
>>> It's possible it's been created with "new", which means the garbage
>>> collector needs to delete it.
>>
>> let's say we add two classes:
>> class FooA {
>> A a;
>> }
>> class FooPA {
>> A* pa;
>> }
>>
>> For the first case, both the class and the struct share the same
>> lifetime thus when an instance of FooA is GC-ed, the GC would call A's
>> d-tor and allow it to do what-ever (self) cleaning it requires. This
>> means the d-tor will always be called.
> 
> Is that the cases even if the destructor of FooA isn't called?
> 
>> For the second case, The GC will only scan "pa" to find inner class
>> instances but will *not* handle the struct value itself.
>> In order to clean what "pa" points to, you need to explicitly call the
>> destructor yourself.
> 
> Are you saying that the GC won't collect a struct allocated with "new"?
> 
> http://dlang.org/expression.html#NewExpression
> 
> "NewExpressions are used to allocate memory on the garbage collected heap...". I though that everything allocated via the GC was also collected by the GC.

Everything allocated is collected, though not necessarily destructed. In case
of structs, the GC currently doesn't know about the dtors, so those are never
called.

   import std.stdio;
   struct S { ~this() { writeln("never called"); } }
   void main() { S* sp; while (1) sp = new S(); }

Right now you have to use a class if you need dtors for heap allocated
objects.

artur