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2396. underlying_type doesn't say what to do for an incomplete enumeration type

Section: 21.3.8.7 [meta.trans.other] Status: C++17 Submitter: Richard Smith Opened: 2014-06-12 Last modified: 2017-07-30

Priority: 0

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Discussion:

Consider:

enum E {
  e = std::underlying_type<E>::type(1)
};

Clearly this should be ill-formed, but the library section doesn't appear to ban it. Suggestion:

Change in 21.3.8.7 [meta.trans.other] Table 57:

Template: template<class T> struct underlying_type;

Condition: T shall be a complete an enumeration type (7.2)

Comments: […]

[2014-06-16 Rapperswil]

Move to Ready

Proposed resolution:

This wording is relative to N3936.

1. Change Table 57 — "Other transformations" as indicated:

   Table 3 — Other type transformations

   Template	Condition	Comments
   …
   template <class T> struct underlying_type;	T shall be a complete an enumeration type (7.2)	[…]