Using directory specifiers in attribute names

[normanb]

If you create an attribute that includes a directory specifier in the name, e.g. /, then you get the following error;

[TileDB::IO] Error: Cannot open file '/MyArray/__518d0e886c764f4480fb7d457a1f4e4c_1552425763728/path/myattr.tdb'; No such file or directory

Making a note of this as it would be helpful to test the attribute name for invalid characters and throw a more meaningful error.