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Proposed resolution (October, 2019):

Change 7.7 [expr.const] paragraph 3 as follows:

A variable isusable in constant expressions afterits initializing declaration is encountered if it is aconstexpr variable, or it is a constant-initialized variableof reference type or of const-qualified integral orenumeration type. An object or reference isusable inconstant expressions if it is

• a variable that is usable in constantexpressions, or

• a template parameter object(13.2 [temp.param]), or

• a string literal object(5.13.5 [lex.string]), or

• a temporary object of non-volatile const-qualifiedliteral type whose lifetime is extended(6.8.7 [class.temporary]) to that of a variable that is usablein constant expressions, or

• a non-mutable subobject or reference member of any of theabove, or.

• a complete temporary object of non-volatile const-qualifiedintegral or enumeration type that is initialized with aconstant expression.

This resolution also resolvesissue 2439.

[Adopted as a DR at the November, 2019 meeting.]

Consider an example like the following:

  typedef const int CI[3];  constexpr CI &ci = CI{11, 22, 33};  static_assert(ci[1] == 22, "");

This is ill-formed because the lifetime of the array temporarydid not start within the current evaluation. Perhaps we shouldtreat all lifetime-extended temporaries of const-qualified literaltype that are initialized by constant expressions as if they areconstexpr objects?