Re: [eigen] Ref<> Problem

[Gabriel <gnuetzi@xxxxxxxxx>]

Thanks a lot Christoph,

So what kind of strange things might happen:

So with your code, a temporary might be cosntructed by initializing r, 
but because it is generated in the classes scope it is bound to exist 
till struct A destructs?

If we assign elements of type A lets say
A a1;
A a2;
a1 = a2,
MIght be a problem , why?   a1 copied the reference, right? it is still 
valid , but if a2 internally stored a temporary than a1 refers to a 
temporary in a2 which might blow up somewhen ?

Is that the problem?


Thanks a lot!




On 12/04/2014 01:11 AM, Christoph Hertzberg wrote:
> On 04.12.2014 00:14, Gabriel wrote:
> > How can I avoid such errors, and whats the correct way of storing a
> > reference to a Matrix  in a class?
>
> You must avoid that a temporary is constructed which runs out of scope 
> after being assigned to r:
>
>   struct A{
>     // constructor does not generate a temporary:
>     template<class Derived>
>     A(const Eigen::MatrixBase<Derived> & in) : r(in) {}
>     // initializing r might create a temporary but that is stored in r
>
>     Eigen::Ref<const Eigen::MatrixXd> r;
>   };
>
> Be aware that strange things might happen, when you try to copy-assign 
> elements of type A.
>
>
> Christoph