• Suliman (11/11) Jul 29 2016 Use the `destroy` function to finalize an object by calling its
• Cauterite (10/16) Jul 29 2016 `destroy` is mainly about running destructors deterministically.
• Kagamin (5/8) Jul 29 2016 You should call destroy when you want to call the destructor
• Lodovico Giaretta (9/20) Jul 29 2016 Destroy will call the destructors, but memory will not actually
• Jonathan M Davis via Digitalmars-d-learn (5/16) Jul 29 2016 destroy is for when you need to explicitly call the destructor on an obj...

Suliman <evermind live.ru> writes:

Use the `destroy` function to finalize an object by calling its 
destructor. The memory of the object is not immediately 
deallocated, instead the GC will collect the memory of the object 
at an undetermined point after finalization:

class Foo { int x; this() { x = 1; } }
Foo foo = new Foo;
destroy(foo);
assert(foo.x == int.init);  // object is still accessible


But I can't understand if D have GC it should remove objects when 
their life is finished. When I should to call `destroy`? What 
would be if I will not call it?

Cauterite <cauterite gmail.com> writes:

On Friday, 29 July 2016 at 13:18:00 UTC, Suliman wrote:
 But I can't understand if D have GC it should remove objects 
 when their life is finished. When I should to call `destroy`? 
 What would be if I will not call it?

`destroy` is mainly about running destructors deterministically. 
 From the source comments:

 "It's used to destroy an object so that any cleanup which its 
 destructor or finalizer does is done and so that it no longer 
 references any other objects."

For example, your object might allocate a large amount of 
manually-managed memory, and you don't want that allocation 
laying around until the next GC cycle, so you can use `destroy` 
to finalise your object as early as possible to release that 
manually-managed allocation.

If you really want to deallocate the object's own memory, you can 
check out core.memory.GC.query() / core.memory.GC.free().

Kagamin <spam here.lot> writes:

On Friday, 29 July 2016 at 13:18:00 UTC, Suliman wrote:
 But I can't understand if D have GC it should remove objects 
 when their life is finished. When I should to call `destroy`? 
 What would be if I will not call it?

You should call destroy when you want to call the destructor 
deterministically, see 
https://en.wikipedia.org/wiki/Resource_management_%28computing%29 
- compare with automatic resource management.

Lodovico Giaretta <lodovico giaretart.net> writes:

On Friday, 29 July 2016 at 13:18:00 UTC, Suliman wrote:
 Use the `destroy` function to finalize an object by calling its 
 destructor. The memory of the object is not immediately 
 deallocated, instead the GC will collect the memory of the 
 object at an undetermined point after finalization:

 class Foo { int x; this() { x = 1; } }
 Foo foo = new Foo;
 destroy(foo);
 assert(foo.x == int.init);  // object is still accessible


 But I can't understand if D have GC it should remove objects 
 when their life is finished. When I should to call `destroy`? 
 What would be if I will not call it?

Destroy will call the destructors, but memory will not actually 
be deallocated before the next GC cycle. It is used because the 
GC cycle does not guarantee to run the destructors, so using 
destroy the destructor is ran immediately (guaranteed). Then, on 
next GC iteration, the memory will be freed. Until then, 
referencing it will not cause segfault, but will cause undefined 
behaviour, as after a destructor the state of the object is 
undefined (I think).

Jonathan M Davis via Digitalmars-d-learn writes:

On Friday, July 29, 2016 13:18:00 Suliman via Digitalmars-d-learn wrote:
 Use the `destroy` function to finalize an object by calling its
 destructor. The memory of the object is not immediately
 deallocated, instead the GC will collect the memory of the object
 at an undetermined point after finalization:

 class Foo { int x; this() { x = 1; } }
 Foo foo = new Foo;
 destroy(foo);
 assert(foo.x == int.init);  // object is still accessible


 But I can't understand if D have GC it should remove objects when
 their life is finished. When I should to call `destroy`? What
 would be if I will not call it?

destroy is for when you need to explicitly call the destructor on an object.
It destroys it without freeing the memory. There are some rare cases where
that is extremely useful, but odds are, you'll never need it.

- Jonathan M Davis