Runtime Type Identification (RTTI)

In compatibility mode, RTTI is off by default, as with the 4.2 compiler. In standard mode, RTTI is on and cannot be turned off. Under the old ABI, RTTI has a noticeable cost in extra data size and in compilation efficiency. (RTTI could not be implemented directly under the old ABI, and an inefficient indirect method was required.) In standard mode, using the new ABI, RTTI has negligible cost. (This is one of several improvements in the ABI.)