Title
Default arguments and signatures of standard library non-member functions
Status
new
Section
[global.functions]
Submitter
Jiang An

Created on 2024-05-11.00:00:00 last changed 1 month ago

Messages

Date: 2024-05-12.12:03:21

Proposed resolution:

This wording is relative to N4981.

  1. Modify [global.functions] as indicated:

    […]

    -2- A call to a non-member function signature described in [support] through [thread] and [depr] shall behave as if the implementation declared no additional non-member function signatures. However, for each non-member function specified with at least one default argument, an implementation may declare additional function signatures with one or more trailing parameters that have default arguments removed.

    [Example 1: The following program is possibly ill-formed because of ambiguity in overload resolution.

    #include <cstddef>
    #include <string>
    
    // One overload of std::stoi ([string.conversions]) is specified as
    // int stoi(const string& str, size_t* idx = nullptr, int base = 10);
    // An implementation can declare these overloads instead of using default arguments:
    // int stoi(const string& str, size_t* idx, int base);
    // int stoi(const string& str, size_t* idx);
    // int stoi(const string& str);
    
    namespace usr {
      int stoi(const std::string&);
      int stoi(const std::string&, std::size_t*);
    }
    
    int main() {
      using std::stoi;
      using usr::stoi;
      int (*p1)(const std::string&) = stoi;                 // possibly ill-formed
      int (*p2)(const std::string&, std::size_t*) = stoi;   // possibly ill-formed
    }
    

    — end example]

Date: 2024-05-11.00:00:00

Currently, std::from_chars and std::to_chars are specified with default arguments. Some implementors want to split them into more overloads to determine the base 10 at compile time (LLVM issue #91268). However, the current standard wording doesn't clearly allow such technique.

History
Date User Action Args
2024-05-12 12:03:21adminsetmessages: + msg14138
2024-05-11 00:00:00admincreate