This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115d. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-10-26

390. Pure virtual must be defined when implicitly called

[Voted into WP at March 2004 meeting.]

In 11.7.4 [class.abstract] paragraph 2, it reads:

A pure virtual function need be defined only if explicitly called with the qualified-id syntax (_N4567_.5.1.1 [expr.prim.general]).

This is IMHO incomplete. A dtor is a function (well, a "special member function", but this also makes it a function, right?) but it is called implicitly and thus without a qualified-id syntax. Another alternative is that the pure virtual function is called directly or indirectly from the ctor. Thus the above sentence which specifies when a pure virtual function need be defined ("...only if...") needs to be extended:

A pure virtual function need be defined only if explicitly called with the qualified-id syntax (_N4567_.5.1.1 [expr.prim.general]) or if implicitly called (11.4.7 [class.dtor] or 11.9.5 [class.cdtor]).

Proposed resolution:

Change 11.7.4 [class.abstract] paragraph 2 from

A pure virtual function need be defined only if explicitly called with the qualified-id syntax (_N4567_.5.1.1 [expr.prim.general]).

to

A pure virtual function need be defined only if explicitly called with, or as if with (11.4.7 [class.dtor]), the qualified-id syntax (_N4567_.5.1.1 [expr.prim.general]).

Note: 11.4.7 [class.dtor] paragraph 6 defines the "as if" cited.