Can you ELI5 why the celltype should be in the CellCache (and why it should be a union)?

Having a union might be an issue for the GPU stuff. We are currently working towards making CellCache type stable for the GPU (xref #1049 (comment)).

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Needed to support reinit! for vector interpolations using the CellIterator.

Union: the grid has a Union, the cellCache not, but the constructor should be type unstable. Iteration is not.

Thanks!

Needed to support reinit! for vector interpolations using the CellIterator.

reinit! acts on some FEValues and you can obtain the information from the geometric interpolation, right?

reinit! acts on some FEValues and you can obtain the information from the geometric interpolation, right?

The actual cell is required to determine the global direction of faces or edges based on its node ids during reinit of FEValues with non-identity mappings.

Couldn't the cell be looked up in reinit! instead? We have the cellid

Couldn't the cell be looked up in reinit! instead? We have the cellid

Yes, would be possible. But that felt like a split design, to partly reinit the cell cache, and then do more lookup based on the grid in the cache during reinit of the fe values.

And also not sure if there are performance pitfalls regarding type stability here, especially for GPU if a Union isn't allowed during reinit!, but haven't checked/thought carefully about this yet.

We should not consider type params as part of the API so this is not breaking.