On 12/14/2015 5:53 PM, Emil Dotchevski wrote:
On Mon, Dec 14, 2015 at 4:46 AM, Agustín K-ballo Bergé < kaballo86@hotmail.com> wrote:
On 12/13/2015 9:07 PM, Emil Dotchevski wrote:
On Sun, Dec 13, 2015 at 1:16 PM, Agustín K-ballo Bergé < kaballo86@hotmail.com> wrote:
On 12/13/2015 5:13 PM, Emil Dotchevski wrote:
Yes, I'm interested to understand what brought this comment, though I am
not sure that there is a solution. The problem is that QVM can't invoke constructors (other than the default constructor) for user-defined types, because different types could have different constructors (believe me, I've seen game programmers define some crazy matrix/vector constructors). Because functions like normalized() operate on user-defined types, they use the default constructor to make a local object before returning it by value.
There's always the copy constructor, which I believe is already implicitly required by the library. Have you experimented with this before?
Actually, there might not be a copy constructor. In QVM views are non-copyable. For example the return type of qvm::row and qvm::col, which present a row or a column of a matrix as a vector, return non-copyable types (which are still valid arguments for the normalized() function in question.)
Anyways, I imagine calling `normalized` with one of those views either won't return something of that view's type, or it won't default-construct a view. Am I close here?
Calling normalized() on a view returns a type deduced by deduce_v, the default for views being a compatible instantiation of the qvm::vec<> template. Such types are required to be copyable and to have accessible default constructor.
Nod, this is one of the unsurprising cases I mentioned. Reinstating some snipped context:
Now I vaguely recall something about being able to explicitly specify the return type, or specializing some kind of deduction facilities, or at least another place were one wouldn't have a source value to copy from, where a default construction would be unsurprising.
if the compiler says there is an error here because `normalized` needs a default constructor, I'm gonna start suspecting something wrong is going on with the library. This is what I would naively expect `normalized` to be doing:
template <typename Vec> Vec normalized(Vec v) { return v /= length(v); }
It can't be implemented that way because the type of the argument might not be copyable.
Does this mean that the library explicitly supports movable-only types? That's somewhat unexpected, given that the library requires all type information necessary for embedded storage, but it's not a bad thing. It would be good to add this information to the reference documentation. Regards, -- Agustín K-ballo Bergé.- http://talesofcpp.fusionfenix.com