I'm pretty confused why the following code doesn't work as expected.

GetValue is a struct.

  auto value = GetValue();
  memcpy(&value, &val, Val.sizeof);

But if I plug in value direct to memset it works!!

  memcpy(&GetValue(), &val, Val.sizeof);

GetValue returns memory to stick a value in and the memcpy is copying it over. It is very confusing logic. Should I not expect the two cases two be identical?

I think that the assignment in the first case is not assigning the reference returned by auto ref GetValue().

I am expecting it to work like a pointer,

  void* value = &GetValue();
  memcpy(value, &val, Val.sizeof);

so to speak but it works more like

    S value;
    value = GetValue();
    memcpy(&value, &val, Val.sizeof);

which copies the data to the memory created for value and not the one returned by GetValue.

On 14/07/2016 6:23 PM, Gorge Jingale wrote:
> I'm pretty confused why the following code doesn't work as expected.
>
> GetValue is a struct.
>
>   auto value = GetValue();
>   memcpy(&value, &val, Val.sizeof);
>
> But if I plug in value direct to memset it works!!
>
>   memcpy(&GetValue(), &val, Val.sizeof);
>
> GetValue returns memory to stick a value in and the memcpy is copying it
> over. It is very confusing logic. Should I not expect the two cases two
> be identical?
>
> I think that the assignment in the first case is not assigning the
> reference returned by auto ref GetValue().
>
> I am expecting it to work like a pointer,
>
>   void* value = &GetValue();
>   memcpy(value, &val, Val.sizeof);
>
> so to speak but it works more like
>
>     S value;
>     value = GetValue();
>     memcpy(&value, &val, Val.sizeof);
>
> which copies the data to the memory created for value and not the one
> returned by GetValue.

Please provide the definitions of GetValue and Val.

On Thursday, 14 July 2016 at 06:23:15 UTC, Gorge Jingale wrote:
> I think that the assignment in the first case is not assigning the reference returned by auto ref GetValue().

Yep. There's no such thing as C++ `auto& val = GetValue()` in D. You'd have to use a pointer instead: `auto pVal = &GetValue()`.

On Thursday, 14 July 2016 at 06:23:15 UTC, Gorge Jingale wrote:
> I think that the assignment in the first case is not assigning the reference returned by auto ref GetValue().


`ref` in D is shallow, it only applies to the thing it is specifically on and is lost across assignments. Once you assign a ref to a new variable, it isn't ref anymore.

> I am expecting it to work like a pointer,

If you need a pointer, use a pointer! ref is a different thing.