This is a generalization of QPrivateSlotObject's FunctionStorage. Changes from the old API: - uses a more neutral API (s/func/object/) - preserves cv-qualifiers and value categories - preserves constexpr'ness - adds a disambiguation tag (e.g. for use in a compressed_pair). The main feature is that it transparently uses the empty base-class optimization to stow away empty classes without allocating separate bytes for them. To be used for the public QSlotObject and QGenericRunnable, at least, so finally pulled the trigger and made it a separate component. Change-Id: I9a13bbdd1dcf64aaf5fc7b2d40a60050d61800b6 Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>