3396. Clarify point of reference for source_location::current() (DE 169)

Section: 17.8.2.2 [support.srcloc.cons] Status: C++20 Submitter: Jens Maurer Opened: 2020-02-13 Last modified: 2021-02-25

Priority: 2

View all issues with C++20 status.

Discussion:

Addresses DE 169

The expectation of the note that a default argument expression involving current() causes a source_location to be constructed that refers to the site of a function call where that default argument is needed has no basis in normative text. In particular, 9.2.3.6 paragraph 5 seems to imply that the name "current" and its semantics are bound where it appears lexically in the function declaration.

Proposed change:

Add normative text to express the desired semantics.

[2020-02 Moved to Immediate on Thursday afternoon in Prague.]

Proposed resolution:

This wording is relative to N4849.

1. Modify 17.8.2.2 [support.srcloc.cons] as indicated:

   static consteval source_location current() noexcept;
   

   -1- […]

   -2- Remarks: When a default member initializer is used to initialize a non-static data member, any calls to currentAny call to current that appears as a default member initializer (11.4 [class.mem]), or as a subexpression thereof, should correspond to the location of the constructor definition or aggregate initialization that initializes the memberuses the default member initializer. Any call to current that appears as a default argument (9.3.4.7 [dcl.fct.default]), or as a subexpression thereof, should correspond to the location of the invocation of the function that uses the default argument (7.6.1.3 [expr.call]).

   -3- [Note: When used as a default argument (9.3.4.7 [dcl.fct.default]), the value of the source_location will be the location of the call to current at the call site. — end note]