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3065. LWG 2989 missed that allpath's other operators should be hidden friends as well

Section: 31.12.6.8[fs.path.nonmember]Status:C++20Submitter: Billy O'Neal IIIOpened: 2018-02-13Last modified: 2021-02-25

Priority:2

View all issues withC++20 status.

Discussion:

Consider the following program:

//See godbolt link#include <assert.h>#include <string>#include <filesystem>using namespace std;using namespace std::filesystem;int main() {  bool b = L"a//b" == std::string("a/b");  assert(b); // passes. What?!  return b;}

L"a" gets converted into apath, and the string gets converted into apath, and then those paths are compared for equality. Butpath equality comparison doesn't work anything like string equality comparison, leading to surprises.

path's other operators should be made hidden friends as well, so that one side or the other of a given operator is of typepath before those conversions apply.

[2018-02-20, Priority set to 2 after mailing list discussion]

[2018-08-23 Batavia Issues processing]

Status to Tentatively Ready

[2018-11, Adopted in San Diego]

Proposed resolution:

This wording is relative toN4713.

All drafting notes from LWG2989⁽ⁱ⁾ apply here too.

1. Modify 31.12.4[fs.filesystem.syn], header<filesystem> synopsis, as indicated:

   […]// 31.12.6.8[fs.path.nonmember], path non-member functionsvoid swap(path& lhs, path& rhs) noexcept;size_t hash_value(const path& p) noexcept;bool operator==(const path& lhs, const path& rhs) noexcept;bool operator!=(const path& lhs, const path& rhs) noexcept;bool operator< (const path& lhs, const path& rhs) noexcept;bool operator<=(const path& lhs, const path& rhs) noexcept;bool operator> (const path& lhs, const path& rhs) noexcept;bool operator>=(const path& lhs, const path& rhs) noexcept;path operator/ (const path& lhs, const path& rhs);[…]

2. Modify 31.12.6.8[fs.path.nonmember] as indicated:

   […]friend bool operator< (const path& lhs, const path& rhs) noexcept;[…]friend bool operator<=(const path& lhs, const path& rhs) noexcept;[…]friend bool operator> (const path& lhs, const path& rhs) noexcept;[…]friend bool operator>=(const path& lhs, const path& rhs) noexcept;[…]friend bool operator==(const path& lhs, const path& rhs) noexcept;[…]friend bool operator!=(const path& lhs, const path& rhs) noexcept;[…]friend path operator/ (const path& lhs, const path& rhs);[…]

3. Modify 31.12.6[fs.class.path], classpath synopsis, as indicated:

   class path {public:  […]// 31.12.6.5.5[fs.path.modifiers], modifiers  […]// 31.12.6.8[fs.path.nonmember], non-member operatorsfriend bool operator< (const path& lhs, const path& rhs) noexcept;friend bool operator<=(const path& lhs, const path& rhs) noexcept;friend bool operator> (const path& lhs, const path& rhs) noexcept;friend bool operator>=(const path& lhs, const path& rhs) noexcept;friend bool operator==(const path& lhs, const path& rhs) noexcept;friend bool operator!=(const path& lhs, const path& rhs) noexcept;friend path operator/ (const path& lhs, const path& rhs);// 31.12.6.5.6[fs.path.native.obs], native format observers  […]};