On 07/14/2014 10:35 AM, ponce wrote:
> Ok, solved it, I just use pointer casts and it seems to work when the
> struct is sliced.
I think there is a terminology issue here. Slicing cannot be undone;
once the object is sliced, the non-A parts are gone.
> On Monday, 14 July 2014 at 13:23:57 UTC, ponce wrote:
>> Hi,
>>
>> I am porting C++ code that undo "Object Slicing" by casting
>> const-references:
>> http://en.wikipedia.org/wiki/Object_slicing
>>
>>
>> My translation in D Code
>> ----
>>
>> struct A
>> {
>> // stuff
>> }
>>
>> struct B
>> {
>> A a;
>> alias a this;
>> // stuff
>> }
>>
>> void myFunction(ref const(A) a)
>> {
>> if (<a-is-actually-a-B>)
>> {
>> // here goes the converstion to a B reference
>> myFunction2(*cast(const(B)*)(&a)); // using pointer to do
>> type-punning
>> }
>> }
>>
>> ----
>>
>>
>> To do this, I need to by guaranteed an object passed through ref
>> const(A) is never, ever passed by value. Is it safe to assume?
It is guaranteed by the language spec that yes, myFunction() takes an A
by reference. However, you can't know where that A is coming from; so,
the safety of that cast is up to you. Consider:
void foo(A a) // <-- Already sliced
{
myFunction(a); // <-- Will perform invalid cast
}
Ali
