Re:Announcing TypeScript 1.6
by WorldMaker on Thursday September 17, 2015 @09:39AM
(#10233247)
It is referring to mathematical sets, but at the categorization of types level rather than the "shape" of types.
If you think of Set X consisting of all the objects that could possibly be built as Class X and Set Y as all the objects that could possibly be built as Class Y, then the union of those sets is all of the Class X derived objects and all of the Class Y derived objects, whereas the intersection of those sets are whatever objects manage to implement or derive from both Class X and Class Y.
If you think of Set X consisting of all the objects that could possibly be built as Class X and Set Y as all the objects that could possibly be built as Class Y, then the union of those sets is all of the Class X derived objects and all of the Class Y derived objects, whereas the intersection of those sets are whatever objects manage to implement or derive from both Class X and Class Y.