CWG Issue 2126 (original) (raw)

This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 118e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-11-05

2126. Lifetime-extended temporaries in constant expressions

Section: 7.7 [expr.const]Status: C++20Submitter: Richard SmithDate: 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 areconstexpr 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.