Created on 2000-05-04.00:00:00 last changed 77 months ago
Rationale (February, 2014):
EWG determined that no action should be taken on this issue.
Rationale (February, 2012):
In light of the nontrivial implementation issues such a change would raise, as well as the fact that this restriction has been accepted into the C++ design lexicon for many years, CWG decided not to make a change at this point. Further consideration, if any, should occur within EWG.
According to 13.4 [class.abstract] paragraph 6,
Member functions can be called from a constructor (or destructor) of an abstract class; the effect of making a virtual call (13.3 [class.virtual]) to a pure virtual function directly or indirectly for the object being created (or destroyed) from such a constructor (or destructor) is undefined.
This prohibition is unnecessarily restrictive. It should not apply to cases in which the pure virtual function has been defined.
Currently the "pure" specifier for a virtual member function has two meanings that need not be related:
The prohibition of virtual calls to pure virtual functions arises from the first meaning and unnecessarily penalizes those who only need the second.
For example, consider a scenario such as the following. A class B is defined containing a (non-pure) virtual function f that provides some initialization and is thus called from the base class constructor. As time passes, a number of classes are derived from B and it is noticed that each needs to override f, so it is decided to make B::f pure to enforce this convention while still leaving the original definition of B::f to perform its needed initialization. However, the act of making B::f pure means that every reference to f that might occur during the execution of one of B's constructors must be tracked down and edited to be a qualified reference to B::f. This process is tedious and error-prone: needed edits might be overlooked, and calls that actually should be virtual when the containing function is called other than during construction/destruction might be incorrectly changed.
Suggested resolution: Allow virtual calls to pure virtual functions if the function has been defined.
|2014-03-03 00:00:00||admin||set||messages: + msg4979|
|2014-03-03 00:00:00||admin||set||status: extension -> nad|
|2012-02-27 00:00:00||admin||set||messages: + msg3865|
|2012-02-27 00:00:00||admin||set||status: open -> extension|