Unexpected behavior when using both alias this and object pointer

[xiren7 via Digitalmars-d-learn]

Thanks. Ali.
My previous post is not clear that I have to store class 
reference(object pointer) in void*.

My actual code is try to use libuv in D.

// genarated from uv.h, only two fields is used: 'data', 'type'.
// the document of 'data': "Space for user-defined arbitrary 
data. libuv does not use this field".
// uv_timer_t is the subclass of uv_handle_t in C. (uv_timer_t 
has all the fields defined in uv_handle_t)
struct uv_handle_t {align(8):
     union {
         struct {void* data; void* _; uv_handle_type type;}
         ubyte[96] _payload;
     }
}
struct uv_timer_t {align(8):
     union {
         struct {void* data; void* _; uv_handle_type type;}
         ubyte[160] _payload;
     }
}
...

// try to resemble the libuv object defined in C.
struct UVHandle {
     uv_handle_t _uvHandle;
     // subclass uv_handle_t
     alias _uvHandle this;

     void close() { // uv_close(&this) }
     bool isClosing() { // uv_is_closing(&this) }
     ...
}

// define Timer as 'final class', in order to force Timer 
allocated in gc.
final class Timer {
     UVHandle* uvHandle
     // subclass UVHandle
     alias uvHandle this;
     ...

     this()
     {
         // malloc memory(nogc) for uv_timer_t.
         uvHandle = malloc(uv_timer_t.sizeof)

         // store the timer object reference in 'data',
         // but 'alias uvHandle this' also overrides 'cast',
         // this is the problem described as my previous post.
         uvHandle.data = cast(void*) this;
     }
     ~this() { free(uvHandle); }

     void start(...) { // uv_timer_start(this.uvHandle, ...) }
     void stop() { // uv_timer_stop(this.uvHandle) }
     ...
}

My current solution is using 'mixin template' instead of 'alias 
this' as the way to subclass:

mixin template UVHandle() { ... }
public final class Timer {
     mixin UVHandle;
     ...
}