Eigen cast AlignedBox double to AlignedBox int-CodePudding

I'm trying to use Eigen AlignedBox. Specifically, I'm trying to cast a box of double into an int one, by using AlignedBox::cast

AlignedBox<double, 2> aabbox2d = AlignedBox<double, 2>(Vector2d(0.52342, 2.12315), Vector2d(3.87346, 4.72525));
aabbox2d.cast<AlignedBox<int, 2>>();
auto minx = aabbox2d.min().x();

Anyway, when the execution gets to min() I get an assert:

Assertion failed: (((SizeAtCompileTime == Dynamic && (MaxSizeAtCompileTime==Dynamic || size<=MaxSizeAtCompileTime)) || SizeAtCompileTime == size) && size>=0), function resize, file /Users/max/Developer/Stage/Workspace/AutoTools3D/dep/libigl/external/eigen/Eigen/src/Core/PlainObjectBase.h, line 312.

Note that this is different from casting a matrix scalar to another one. An object is implied. Supposedly I'm not doing the cast correctly. Does someone know the right way? Thank you

CodePudding user response：

Consulting the documentation for AlignedBox::cast shows that the template argument to cast is defined as template<typename NewScalarType> and the return value is *this with scalar type casted to NewScalarType. Thus the cast function does not modify the existing instance of the box, but returns a new one. To make your example work you need to store the returned instance like follows:

AlignedBox<double, 2> aabbox2d = AlignedBox<double, 2>(Vector2d(0.52342, 2.12315), Vector2d(3.87346, 4.72525));
AlignedBox<int, 2>  casted = aabbox2d.cast<int>();
const int minx = casted.min().x();

You can play with this here: https://godbolt.org/z/ozE4rzebb

As a side note: as the documentation states, when working with Eigen one should refrain from using auto (probably not a problem in this case though)