object - interface compatibility

[BCS]

Frank Benoit (keinfarbton) wrote:
> Today I had a hard lesson to learn. An iface and an object is not
> exchangeable. The reference to an object is manipulated if it is casted
> to an interface type.
> 
> This happens implicit if an object is passed to a var/meth which wants
> it to be type of iface.
> 
> But this does not happen implicit if you want to pass and array of
> objects. This is, because it would mean to iterate over the array, cast
> piece-wise and build a new array.
> But the consequence is, that the user of the class has to distinguish
> between class types and iface types.
> 
> I wonder if this should really be in that way?
> Is this documented?

The convention from an object to an interface is unavoidable (at some 
point). Making this conversion implicit would help but, could get costly.


interface I{}
class C : I{}

foo(I[] arr){}



fig(C[] arr){}
{
	foo(cast(I[])arr);
}


void main()
{
	C[] blah = new C[1000000];

	fig(blah); // Ouch O(n) cost in a cast
}



you can neaten up code a bit with something like this:

If[] acast(If, Cl)(Cl[] arr)
{
	If[] ret = new If[arr.length];
	foreach(i,e;arr)
		ret[i] = cast(If)arr[i];

	return ret;
}