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1766. Values outside the range of the values of an enumeration

Section: 9.7.1  [dcl.enum]     Status: CD4     Submitter: CWG     Date: 2013-09-23

[Moved to DR at the November, 2014 meeting.]

Although issue 1094 clarified that the value of an expression of enumeration type might not be within the range of the values of the enumeration after a conversion to the enumeration type (see [expr.static.cast] paragraph 10), the result is simply an unspecified value. This should probably be strengthened to produce undefined behavior, in light of the fact that undefined behavior makes an expression non-constant. See also 11.4.10 [class.bit] paragraph 4.

Proposed resolution (February, 2014):

Change [expr.static.cast] paragraph 10 as follows:

A value of integral or enumeration type can be explicitly converted to an enumeration type. The value is unchanged if the original value is within the range of the enumeration values (9.7.1 [dcl.enum]). Otherwise, the resulting value is unspecified (and might not be in that range) behavior is undefined. A value of floating-point type...