• Gorge Jingale (21/21) Jul 13 2016 I'm pretty confused why the following code doesn't work as
• rikki cattermole (2/22) Jul 13 2016 Please provide the definitions of GetValue and Val.
• kink (3/5) Jul 14 2016 Yep. There's no such thing as C++ `auto& val = GetValue()` in D.
• Adam D. Ruppe (5/8) Jul 14 2016 `ref` in D is shallow, it only applies to the thing it is

Gorge Jingale <Frifj mail.com> writes:

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.

rikki cattermole <rikki cattermole.co.nz> writes:

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.

kink <noone nowhere.com> writes:

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()`.

Adam D. Ruppe <destructionator gmail.com> writes:

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.