This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-08-11
2126. Lifetime-extended temporaries in constant expressionsSection: 7.7 [expr.const] Status: C++20 Submitter: Richard Smith Date: 2015-05-20[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 temporary did not start within the current evaluation. Perhaps we should treat all lifetime-extended temporaries of const-qualified literal type that are initialized by constant expressions as if they are constexpr objects?
Proposed resolution (October, 2019):
Change 7.7 [expr.const] paragraph 3 as follows:
A variable is usable in constant expressions after its initializing declaration is encountered if it is a constexpr variable, or it is a constant-initialized variable of reference type or of const-qualified integral or enumeration type. An object or reference is usable in constant expressions if it is
a variable that is usable in constant expressions, 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-qualified literal type whose lifetime is extended (6.8.7 [class.temporary]) to that of a variable that is usable in constant expressions, or
a non-mutable subobject or reference member of any of the above , or .
a complete temporary object of non-volatile const-qualified integral or enumeration type that is initialized with a constant expression.
This resolution also resolves issue 2439.
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