This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

2715. "calling function" for parameter initialization may not exist

[Accepted as a DR at the June, 2023 meeting.]

Subclause 7.6.1.3 [expr.call] paragraph 6 specifies:

... The initialization and destruction of each parameter occurs within the context of the calling function. [Example 2: The access of the constructor, conversion functions or destructor is checked at the point of call in the calling function. If a constructor or destructor for a function parameter throws an exception, the search for a handler starts in the calling function; in particular, if the function called has a function-try-block (14.1 [except.pre]) with a handler that can handle the exception, this handler is not considered. —end example]

However, there is no calling function in the case where a function call appears in the initializer of a namespace-scope variable. Likewise, some constant expressions appearing in a type-id do not have calling functions, either. For example:

  class C {
   private:
    constexpr int C(int) {}
    friend void foo(int (*a)[1]) noexcept;
  };

  constexpr int bar(C) { return 1; }

  void foo(int (&a)[bar(1)]) noexcept(bar(2) > 0); // presumably OK because of friendship

Proposed resolution (approved by CWG 2023-04-28):

Change in 7.6.1.3 [expr.call] paragraph 6 as follows:

... The initialization and destruction of each parameter occurs within the context of the calling function full-expression (6.9.1 [intro.execution]) where the function call appears. [Example 2: The access (11.8.1 [class.access.general]) of the constructor, conversion functions, or destructor is checked at the point of call in the calling function. If a constructor or destructor for a function parameter throws an exception, the search for a handler starts in the calling function; in particular, if the function called has a any function-try-block (14.1 [except.pre]) of the called function with a handler that can handle the exception, this handler is not considered. —end example]