This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-11-11

2166. Unclear meaning of “undefined constexpr function”

Section: 7.7  [expr.const]     Status: drafting     Submitter: Howard Hinnant     Date: 2015-08-05

According to 7.7 [expr.const] bullet 5.4, an expression is a constant expression unless (among other reasons) it would evaluate

This does not address the question of the point at which a constexpr function must be defined. The intent, in order to allow mutually-recursive constexpr functions, was that the function must be defined prior to the outermost evaluation that eventually results in the invocation, but this is not clearly stated.