Reuse object memory?

[Namespace via Digitalmars-d-learn]

On Sunday, 19 April 2015 at 21:17:18 UTC, Ali Çehreli wrote:
> On 04/19/2015 09:04 AM, Namespace wrote:
>
> > Is it somehow possible to reuse the memory of an object?
>
> Yes, when you cast a class variable to void*, you get the 
> address of the object.
>
> > @nogc
> > T emplace(T, Args...)(ref T obj, auto ref Args args) nothrow
> if (is(T ==
> > class)) {
>
> There is already std.conv.emplace:
>
> import std.conv;
> import core.memory;
>
> class Foo
> {
>     int i;
>
>     this(int i)
>     {
>         this.i = i;
>     }
> }
>
> void main()
> {
>     void* buffer = GC.calloc(1234);
>
>     enum FooSize = __traits(classInstanceSize, Foo);
>
>     /* These two object are constructed on a void[] slice: */
>     auto f = emplace!Foo(buffer[0..FooSize], 42);
>     auto f2 = emplace!Foo(buffer[0..FooSize], 43);
>
>     /* f3 is constructed on top of an existing object: */
>     auto f2_addr = cast(void*)f2;
>     auto f3 = emplace!Foo(f2_addr[0..FooSize], 44);
>
>     /* At this point, all three reference the same object: */
>     assert(&f.i == &f2.i);
>     assert(&f.i == &f3.i);
> }
>
> Ali

I'm sorry if I annoy you, but I would really like to know how you 
would reuse already instantiated storage of an existing object.

Example code:
----
final class Foo {
     uint id;

     @nogc
     this(uint id) {
         this.id = id;
     }
}

Foo f = new Foo(42);
----