# common implementation for `collect_mclassdefs`, `collect_mclasses`, and `collect_mtypes`.
	private fun collect_things(mmodule: MModule)
	do
		var res = new HashSet[MClassDef]
		var seen = new HashSet[MClass]
		var types = new HashSet[MClassType]
		seen.add(self.mclass)
		var todo = [self.mclass]
		while not todo.is_empty do
			var mclass = todo.pop
			#print "process {mclass}"
			for mclassdef in mclass.mclassdefs do
				if not mmodule.in_importation <= mclassdef.mmodule then continue
				#print "  process {mclassdef}"
				res.add(mclassdef)
				for supertype in mclassdef.supertypes do
					types.add(supertype)
					var superclass = supertype.mclass
					if seen.has(superclass) then continue
					#print "    add {superclass}"
					seen.add(superclass)
					todo.add(superclass)
				end
			end
		end
		collect_mclassdefs_cache[mmodule] = res
		collect_mclasses_cache[mmodule] = seen
		collect_mtypes_cache[mmodule] = types
	end