It's not uncommon to dispatch on 3 or more arguments. Linear algebra specializations are one case where I tend to do this a lot, for example specializing on str

It's not uncommon to dispatch on 3 or more arguments. Linear algebra specializations are one case where I tend to do this a lot, for example specializing on structured matrix types (block banded matrices) against non-standard vectors (GPU arrays), you then need to specialize on the output vector to make it non-ambiguous in many cases.