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3131. addressof all the things

Section: 30.13 [time.parse], 27.4.3.8.1 [string.accessors], 27.3.3 [string.view.template], 23.2.2 [container.requirements.general], 24.3.5.4 [output.iterators], 24.3.5.6 [bidirectional.iterators], 28.6.6 [re.traits], 28.6.11.1 [re.regiter], 32.6.5.2 [thread.lock.guard] Status: C++20 Submitter: Tim Song Opened: 2018-06-30 Last modified: 2021-02-25

Priority: 0

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Discussion:

Some additional instances where the library specification applies unary operator & when it should use addressof.

[2018-07-20 Status to Tentatively Ready after five positive votes on the reflector.]

[2018-11, Adopted in San Diego]

Proposed resolution:

This wording is relative to N4750.

[Drafting note: Two uses of & in 24.5.1 [reverse.iterators] are not included in the wording below because the entire sentence is slated to be removed by a revision of P0896, the One Ranges Proposal.]

1. Change 30.13 [time.parse] p4-5 as indicated:

   template<class charT, class traits, class Alloc, class Parsable>
     unspecified
       parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp,
             basic_string<charT, traits, Alloc>& abbrev);
   

   -4- Remarks: This function shall not participate in overload resolution unless

   from_stream(declval<basic_istream<charT, traits>&>(), fmt.c_str(), tp, &addressof(abbrev))
   

   is a valid expression.

   -5- Returns: A manipulator that, when extracted from a basic_istream<charT, traits> is, calls from_stream(is, fmt.c_str(), tp, &addressof(abbrev)).

2. Change 30.13 [time.parse] p8-9 as indicated:

   template<class charT, class traits, class Alloc, class Parsable>
     unspecified
       parse(const basic_string<charT, traits, Alloc>& fmt, Parsable& tp,
             basic_string<charT, traits, Alloc>& abbrev, minutes& offset);
   

   -8- Remarks: This function shall not participate in overload resolution unless

   from_stream(declval<basic_istream<charT, traits>&>(), fmt.c_str(), tp, &addressof(abbrev), &offset)
   

   is a valid expression.

   -9- Returns: A manipulator that, when extracted from a basic_istream<charT, traits> is, calls from_stream(is, fmt.c_str(), tp, &addressof(abbrev), &offset).

3. Change 27.4.3.8.1 [string.accessors] p1 and p4 as indicated:

   const charT* c_str() const noexcept;
   const charT* data() const noexcept;
   

   -1- Returns: A pointer p such that p + i == &addressof(operator[](i)) for each i in [0, size()].

   -2- Complexity: Constant time.

   -3- Requires: The program shall not alter any of the values stored in the character array.

   charT* data() noexcept;
   

   -4- Returns: A pointer p such that p + i == &addressof(operator[](i)) for each i in [0, size()].

   -5- Complexity: Constant time.

   -6- Requires: The program shall not alter the value stored at p + size().

4. Change 27.3.3.4 [string.view.iterators] p4 as indicated:

   constexpr const_iterator begin() const noexcept;
   constexpr const_iterator cbegin() const noexcept;
   

   -4- Returns: An iterator such that

   (4.1) — if !empty(), &addressof(*begin()) == data_,

   (4.2) — otherwise, an unspecified value such that [begin(), end()) is a valid range.

5. Change 27.3.3.8 [string.view.ops] p21 and p24 as indicated:

   constexpr bool starts_with(charT x) const noexcept;
   

   -21- Effects: Equivalent to: return starts_with(basic_string_view(&addressof(x), 1));

   […]

   constexpr bool ends_with(charT x) const noexcept;
   

   -24- Effects: Equivalent to: return ends_with(basic_string_view(&addressof(x), 1));

6. Change 27.3.3.9 [string.view.find] p5 as indicated:

   -5- Each member function of the form

   constexpr return-type F(charT c, size_type pos);
   

   is equivalent to return F(basic_string_view(&addressof(c), 1), pos);

7. Edit 23.2.2 [container.requirements.general], Table 77 — "Container requirements", as indicated:

   Table 77 — Container requirements

   Expression	Return type	Operational semantics	Assertion/note pre/post-condition	Complexity
   […]
   (&a)->a.~X()	void		the destructor is applied to every element of a; any memory obtained is deallocated.	linear
   […]

8. Edit 24.3.5.4 [output.iterators], Table 90 — "Output iterator requirements (in addition to Iterator)", as indicated:

   Table 90 — Output iterator requirements (in addition to Iterator)

   Expression	Return type	Operational semantics	Assertion/note pre/post-condition
   […]
   ++r	X&		&addressof(r) == &addressof(++r). […]
   […]

9. Edit 24.3.5.6 [bidirectional.iterators], Table 92 — "Bidirectional iterator requirements (in addition to forward iterator)", as indicated:

   Table 92 — Bidirectional iterator requirements (in addition to forward iterator)

   Expression	Return type	Operational semantics	Assertion/note pre/post-condition
   --r	X&		[…] &addressof(r) == &addressof(--r).
   […]

10. Change 28.6.6 [re.traits] p6 as indicated:

    template<class ForwardIterator>
      string_type transform(ForwardIterator first, ForwardIterator last) const;
    

    -6- Effects: As if by:

    string_type str(first, last);
    return use_facet<collate<charT>>(
      getloc()).transform(&*str.begindata(), &*str.begindata() + str.length());
    

11. Change 28.6.11.1.2 [re.regiter.cnstr] p2 as indicated:

    regex_iterator(BidirectionalIterator a, BidirectionalIterator b,
                   const regex_type& re,
                   regex_constants::match_flag_type m = regex_constants::match_default);
    

    -2- Effects: Initializes begin and end to a and b, respectively, sets pregex to &addressof(re), sets flags to m, then calls regex_search(begin, end, match, *pregex, flags). If this call returns false the constructor sets *this to the end-of-sequence iterator.

12. Change 28.6.11.1.4 [re.regiter.deref] p2 as indicated:

    const value_type* operator->() const;
    

    -2- Returns: &addressof(match).

13. Change 32.6.5.2 [thread.lock.guard] p2-7 as indicated:

    explicit lock_guard(mutex_type& m);
    

    -2- Requires: If mutex_type is not a recursive mutex, the calling thread does not own the mutex m.

    -3- Effects: As if byInitializes pm with m. Calls m.lock().

    -4- Postconditions: &pm == &m

    lock_guard(mutex_type& m, adopt_lock_t);
    

    -5- Requires: The calling thread owns the mutex m.

    -6- Postconditions: &pm == &mEffects: Initializes pm with m.

    -7- Throws: Nothing.