The most relevant signal member function appears to be connect(), so let's create a wrapper function for that now, without the more esoteric ordering features for now. Move the signal member itself to a new pImpl. The benefits are worth it: preprocessor input reduced by 2.8GB, that's 9% of the total (excluding system headers which are not counted because they don't generate dependencies). Change-Id: I0aaeda51a5630a348bb12c81a83f67afbd508a14