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4581. constant_of(^^v) for variable v of reference to array/function type produces reflection of pointer constant

Section: 21.4.7 [meta.reflection.queries] Status: New Submitter: S. B. Tam Opened: 2026-05-18 Last modified: 2026-09-18

Priority: 2

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Discussion:

After CWG 3111, constant_of uses reflect_constant_array and reflect_function for arrays and functions respectively. But since it inspects type_of(r) and not remove_reference(type_of(r)), variables of reference types will still decay to pointers. It's unclear to me whether this is intended.

[2026-08-27; Reflector poll.]

Set priority to 2 after reflector poll.

May not be possible to avoid decay for array/function references in constant_of, since copies of non-constant arrays can't be constants.

[2026-09-18; Tomasz provides proposed resolution.]

Clarifying behavior of constant_of and reflect_constant_array for objects which values cannot be accessed at compile is left to be handled in separate issues.

Proposed resolution:

This wording is relative to N5054.

1. Modify 21.4.7 [meta.reflection.queries] as indicated:

   consteval info constant_of(info r);
   

   -7- Let R be a constant expression of type info such that R == r is true. If r represents an annotation, then let C be its underlying constant.

   -8- Effects: Equivalent to:

   if constexpr (is_annotation(R)) {
     return C;
   } else if constexpr (is_array_type(remove_reference(type_of(R)))) {
     return reflect_constant_array([: R :]);
   } else if constexpr (is_function_type(remove_reference(type_of(R)))) {
     return reflect_function([: R :]);
   } else {
     return reflect_constant([: R :]);
   }
   

   -9- Throws: meta::exception unless either r represents an annotation or [: R :] is a valid splice-expression (7.5.9 [expr.prim.splice]).