This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 119a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-12-20

3122. Inadequate value-dependence for reflect-expressions

(From submission #808.)

The follow example ought to be value-dependent, but is currently not specified to be so:

  template <typename T>
  consteval void f() {
    T v;
    std::meta::info R = std::meta::type_of(^^v);   // not currently value-dependent
  }

Proposed resolution (approved by CWG 2025-11-21):

Change in 13.8.3.4 [temp.dep.constexpr] paragraph 7 as follows:

A reflect-expression is value-dependent if

• it is of the form ^^reflection-name and either lookup for the reflection-name finds a declaration that inhabits a scope corresponding to a templated entity or the reflection-name is
  • is a dependent qualified name,
  • is a dependent namespace-name, or
  • is the name of a template parameter, or
  • names a dependent member of the current instantiation (13.8.3.2 [temp.dep.type]),
• it is of the form ^^type-id and the type-id denotes a dependent type, or
• it is of the form ^^id-expression and the id-expression is value-dependent.

(Drafting note: Reflection on block-scope externs is made ill-formed by issue 3065.)