A systematic approach for invariants of $C^*$-algebras
We define a categorical framework in which we build a systematic construction that provides generic invariants for $C^*$-algebras. The benefit is significant as we show that any invariant arising this way automatically enjoys nice properties such as continuity, a metric on the set of morphisms and a theory of ideals and quotients which naturally encapsulates compatibility diagrams. Consequently, any of these invariants appear as good candidates for the classification of non-simple $C^*$-algebras. Further, most of the existing invariants could be rewritten via this method. As an application, we define a Hausdorffized version of the unitary Cuntz semigroup and explore its potential towards classification results. We indicate several open lines of research.