Problem with casting instance reference to void* and back.

[Artur Skawina via Digitalmars-d-learn]

On 07/27/15 14:03, Vlad Leberstein via Digitalmars-d-learn wrote:
> Hi! My use case requires interaction with C API which in turn implies storing object instance reference as void *. I'm using gdc 4.9.2 and everything worked fine with "object -> void * -> object" conversion, but "object -> void * -> interface" failed. The stripped-down example is something like this:
> 
> interface TestInterface {
>     void testMethod();
> }
> 
> class TestImpl : TestInterface {
>     void testMethod() {
>         writefln("TestImpl::testMethod\n");
>     }
> };
> 
> void testDispathcer(void *rawSelf) {
>     auto self = cast(TestInterface) rawSelf;
>     // nothing happens
>     self.testMethod();
> }
> 
> 
> int main(string[] args) {
>     auto t = new TestImpl();
>     testDispathcer(cast(void *) t);
>     return 0;
> }

> Is there any way to handle such situation without resorting to templating dispatcher with every *Impl type?

    auto self = cast(TestInterface)cast(Object) rawSelf

[you should probably check for null, and consider using
 a reinterpret-cast (`testDispathcer(*cast(void **)&t)`)
 because a "normal" one can be overridden by the class,
 sometimes accidentally]

artur