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Showing content from https://cplusplus.github.io/LWG/issue3131 below:

Issue 3131: addressof all the things

This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of C++20 status.

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.]

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 )).

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).

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().
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.
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));
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);
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 […]
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 ).
[…] […]
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 ). […]

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());

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.
Change 28.6.11.1.4 [re.regiter.deref] p2 as indicated:
```
const value_type* operator->() const;
```
-2- Returns: & addressof(match ).
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 by Initializes pm with m. Callsm.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 == &m Effects: Initializes pm with m. -7- Throws: Nothing.

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