a default constructor for catmull_rom?

[xarthurx]

When trying to use this catmull_rom as a private member of a class, no matter what type Point is (say Eigen::Vector2d> here), there're always an error said no default constructor exists for class boost::math::catmull_rom<Eigen::Vector2d>".

This usually will not happen to other constructors.

Would it be possible to provide an empty constructor for the class?

[NAThompson]

No, there is no default constructor for the Catmull-Rom class.

This is because the constructor computes the parametrization from the point set geometry. The class is therefore always in a valid state. A default constructor leaves the class in an invalid state.

There's almost always a way around the problem you are encountering, though I do feel your pain!

However, @jzmaddock has vastly more C++ knowledge than myself. John, do you know a clean way to solve this problem of creating a member variable out of a class with no default constructor? IIRC the way to do it is with a pointer member?

(Your code reminds me I should add a unit test for Eigen vectors to the Catmull-Rom tests.)

[xarthurx]

A pointer works, for the constructor.

However, if the class is designed to be used this way, a method similar to at() that works the same as operator() should be provided, similar to what std::vector has.

Otherwise, sth like (*ptrToCatMullCrv)(t) to get the value at t is really wired.

[NAThompson]

at() doesn't work that way: It does bounds checking on an integer index. It would definitely be surprising and non-idiomatic to use it in the way you are suggesting.

Personally, I don't see any problem with (*ptr)(t).

[xarthurx]

OK, I'll use the (*ptr)(t) for now. But IMHO, I don't think this issue is solved yet...