On 01.05.2011 17:30, CrypticMetaphor wrote:
Hi, I've been away from D for a while, but now I'm back and I'm stuck
with an compile time error.
I've got a Matrix33 class and a Vector3 class, but something is wrong
with the way I return my Vector3 in my matrix class:
If I do this I get an error:
Matrix33 mtest = new Matrix33();
mtest.SetIdentity();
Vector3 test1 = new Vector3(0, 0, 0);
Vector3 test2 = test + mtest.GetColumn(2);
I get the error "Error: mtest.GetColumn(x) is not an lvalue"
But the following works:
Matrix33 mtest = new Matrix33();
mtest.SetIdentity();
Vector3 test1 = new Vector3(0, 0, 0);
Vector3 temp = mtest.GetColumn(2);
Vector3 test2 = test + temp;
// GetColumn method
Matrix33
{
// ...
/// Get a matrix column, horizontal line
Vector3 GetColumn(uint index)
{
assert(!(index > 2), "index is too high");
return new Vector3(cell[index * 3], cell[index * 3 + 1],
cell[index * 3 + 2]);
}
// ...
}
My questions:
What changes do I have to make to make the first example compile?
Ehm.. Well, first things first: you shouldn't use classes for
lightweight & plain data things like vectors. There are structs for
that. In general, structs are value-like objects living on the stack
while classes are reference-like objects living on the heap. Your
current code is going to allocate on GC heap new vector in every
GetColumn and I suspect also when adding two vectors.
As for the error I think the reason is in your's Vector's operator +
overloading which expects ref Vector parameter it seems, though you'd
better provide this function code as well.
--
Dmitry Olshansky
