Section: 16.4.6.4 [global.functions] Status: New Submitter: Jiang An Opened: 2024-05-11 Last modified: 2024-08-02
Priority: 3
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Discussion:
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.
[2024-08-02; Reflector poll]
Set priority to 3 after reflector poll. "It's a lot of new text just to say you can't do that, lose the example?" "Might be NAD, is this already disallowed?" "Only for member functions."
Proposed resolution:
This wording is relative to N4981.
Modify 16.4.6.4 [global.functions] as indicated:
[…]
-2- A call to a non-member function signature described in 17 [support] through 32 [thread] and D [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]