This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-04-13

1318. Syntactic ambiguities with final

Section: Clause 11  [class]     Status: CD3     Submitter: Johannes Schaub     Date: 2011-05-14

[Moved to DR at the April, 2013 meeting.]

The ambiguity in an example like

 struct A final { };

is resolved by 5.11 [lex.name] paragraph 2 to be the declaration of a variable named final:

any ambiguity as to whether a given identifier has a special meaning is resolved to interpret the token as a regular identifier.

Similarly, in an example like

 struct C { constexpr operator int() { return 5; } }; struct A { struct B final : C{}; };

final is taken as the name of a bit-field member rather than as the name of a nested class.

Proposed resolution (October, 2012):

  1. Change 5.11 [lex.name] paragraph 2 as follows:

    2. The identifiers in Table 3 have a special meaning when appearing in a certain context. When referred to in the grammar, these identifiers are used explicitly rather than using the identifier grammar production. Unless otherwise specified, any ambiguity as to whether a given identifier has a special meaning is resolved to interpret the token as a regular identifier.

  2. Change Clause 11 [class] paragraph 3 as follows:

    3. If a class is marked with the class-virt-specifierfinal and it appears as a base-type-specifier in a base-clause (11.7 [class.derived]), the program is ill-formed. Whenever a class-key is followed by a class-head-name, the identifierfinal, and a colon or left brace, final is interpreted as a class-virt-specifier. [Example:

     struct A; struct A final {}; // OK: definition of struct A, // not value-initialization of variable final struct X { struct C { constexpr operator int() { return 5; } }; struct B final : C{}; // OK: definition of nested class B, // not declaration of a bit-field member final };

    —end example]



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