libsigc++-2.0-dev binary package in Ubuntu Focal amd64

 This library implements a full callback system for use in widget
 libraries, abstract interfaces, and general programming. It provides
 the ability to connect an abstract callback to a class method,
 function, or function object, and contains adaptor classes for the
 connection of dissimilar callbacks.
 .
 These are the development files for libsigc++, needed only if you
 wish to write software which uses it.

Source package