This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

671. Explicit conversion from a scoped enumeration type to integral type

[Voted into the WP at the September, 2008 meeting.]

There appears to be no provision in the Standard for explicit conversion of a value of a scoped enumeration type to an integral type, even though the inverse conversion is permitted. That is,

    enum class E { e };
    static_cast<E>(0);       // #1: OK
    static_cast<int>(E::e);  // #2: error

This is because values of scope enumeration types (intentionally) cannot be implicitly converted to integral types (7.3.7 [conv.prom] and 7.3.9 [conv.integral]) and 7.6.1.9 [expr.static.cast] was not updated to permit #2, although #1 is covered by paragraph 8.

Proposed resolution (June, 2008):

Add the following as a new paragraph following 7.6.1.9 [expr.static.cast] paragraph 8:

A value of a scoped enumeration type (9.7.1 [dcl.enum]) can be explicitly converted to an integral type. The value is unchanged if the original value can be represented by the specified type. Otherwise, the resulting value is unspecified.