ranges::to eigen about range-v3 HOT 2 OPEN

I'm not familiar with Eigen.

to() was standardized from C++23, you can find the mechanism for how it works here. In short, if C is the destination type and r is the source range, it'll try to do (in order):

1. C(r)
2. C(from_range, r)
3. C(ranges::begin(r), ranges::end(r))
4. C c; /* try to reserve */; ranges::copy(r, /* inserter into c */);
5. A more complicated thing for recursion

It looks like option (4) there might work for Eigen::VectorXd, does it? If so we could try to extend the implementation here to do something similar.

range-v3 right now tries to do

1. C c; r.reserve(ranges::size(r)); c.assign(ranges::begin(r), ranges::end(r));
2. C(ranges::begin(r), ranges::end(r))

from range-v3.

Thanks for all the info!
Indeed option 4 should work with Eigen. Its pretty much what I do in my custom function in the original comment as you noted.

I tried with c++23 std::ranges::to (should've done before) but unfortunately it doesn't compile.
https://godbolt.org/z/rsd8bdEKc
So I am not sure that in the end it would work with ranges-v3 either. Maybe Eigen would need to do something as well.

from range-v3.