that is the concrete example! let me rephrase that. `\__calcAll:n{\itshape}` calculates the alphabet length, the em width and ex-height of a font. I want that data in a table, but also with the same data for `\bfseries` etc.
Instead of having `\__calcAll:n{\itshape} \texttt{itshape}&\dim_use:N\_alph_dim& ...\\\ \__calcAll:n{\bfseries}\texttt{bfseries}&\dim_use:N\_alph_dim&...` and so on, I thought I could optimize the thing