[over.match.funcs] - C++20 → C++23

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@@ -1,28 +1,33 @@
 ### Candidate functions and argument lists <a id="over.match.funcs">[[over.match.funcs]]</a>
 The subclauses of  [[over.match.funcs]] describe the set of candidate
 functions and the argument list submitted to overload resolution in each
 context in which overload resolution is used. The source transformations
 and constructions defined in these subclauses are only for the purpose
 of describing the overload resolution process. An implementation is not
 required to use such transformations and constructions.
 The set of candidate functions can contain both member and non-member
-functions to be resolved against the same argument list. So that
-argument and parameter lists are comparable within this heterogeneous
-set, a member function is considered to have an extra first parameter,
-called the *implicit object parameter*, which represents the object for
-which the member function has been called. For the purposes of overload
-resolution, both static and non-static member functions have an implicit
-object parameter, but constructors do not.
 Similarly, when appropriate, the context can construct an argument list
 that contains an *implied object argument* as the first argument in the
 list to denote the object to be operated on.
-For non-static member functions, the type of the implicit object
 parameter is
 - “lvalue reference to cv `X`” for functions declared without a
   *ref-qualifier* or with the `&` *ref-qualifier*
 - “rvalue reference to cv `X`” for functions declared with the `&&`
@@ -30,44 +35,46 @@ parameter is
 where `X` is the class of which the function is a member and cv is the
 cv-qualification on the member function declaration.
 [*Example 1*: For a `const` member function of class `X`, the extra
-parameter is assumed to have type “reference to
 `const X`”. — *end example*]
-For conversion functions, the function is considered to be a member of
-the class of the implied object argument for the purpose of defining the
-type of the implicit object parameter. For non-conversion functions
-introduced by a *using-declaration* into a derived class, the function
-is considered to be a member of the derived class for the purpose of
-defining the type of the implicit object parameter. For static member
-functions, the implicit object parameter is considered to match any
-object (since if the function is selected, the object is discarded).
 [*Note 1*: No actual type is established for the implicit object
 parameter of a static member function, and no attempt will be made to
 determine a conversion sequence for that parameter
 [[over.match.best]]. — *end note*]
 During overload resolution, the implied object argument is
 indistinguishable from other arguments. The implicit object parameter,
 however, retains its identity since no user-defined conversions can be
-applied to achieve a type match with it. For non-static member functions
-declared without a *ref-qualifier*, even if the implicit object
-parameter is not const-qualified, an rvalue can be bound to the
 parameter as long as in all other respects the argument can be converted
 to the type of the implicit object parameter.
 [*Note 2*: The fact that such an argument is an rvalue does not affect
 the ranking of implicit conversion sequences
 [[over.ics.rank]]. — *end note*]
 Because other than in list-initialization only one user-defined
 conversion is allowed in an implicit conversion sequence, special rules
-apply when selecting the best user-defined conversion (
-[[over.match.best]], [[over.best.ics]]).
 [*Example 2*:
 ``` cpp
 class T {
@@ -82,33 +89,57 @@ public:
 T a = 1;            // error: no viable conversion (T(C(1)) not considered)
 ```
 — *end example*]
 In each case where a candidate is a function template, candidate
 function template specializations are generated using template argument
-deduction ([[temp.over]], [[temp.deduct]]). If a constructor template
-or conversion function template has an *explicit-specifier* whose
 *constant-expression* is value-dependent [[temp.dep]], template argument
-deduction is performed first and then, if the context requires a
-candidate that is not explicit and the generated specialization is
 explicit [[dcl.fct.spec]], it will be removed from the candidate set.
 Those candidates are then handled as candidate functions in the usual
-way.[^2] A given name can refer to one or more function templates and
-also to a set of non-template functions. In such a case, the candidate
-functions generated from each function template are combined with the
-set of non-template candidate functions.
-A defaulted move special member function ([[class.copy.ctor]],
-[[class.copy.assign]]) that is defined as deleted is excluded from the
-set of candidate functions in all contexts. A constructor inherited from
-class type `C` [[class.inhctor.init]] that has a first parameter of type
-“reference to *cv1* `P`” (including such a constructor instantiated from
-a template) is excluded from the set of candidate functions when
-constructing an object of type *cv2* `D` if the argument list has
-exactly one argument and `C` is reference-related to `P` and `P` is
-reference-related to `D`.
 [*Example 3*:
 ``` cpp
 struct A {
@@ -131,10 +162,12 @@ B b3 = C();                             // calls #4
 — *end example*]
 #### Function call syntax <a id="over.match.call">[[over.match.call]]</a>
 In a function call [[expr.call]]
 ``` bnf
 postfix-expression '(' expression-listₒₚₜ ')'
 ```
@@ -144,24 +177,27 @@ template, overload resolution is applied as specified in
 [[over.call.func]]. If the *postfix-expression* denotes an object of
 class type, overload resolution is applied as specified in
 [[over.call.object]].
 If the *postfix-expression* is the address of an overload set, overload
-resolution is applied using that set as described above. If the function
-selected by overload resolution is a non-static member function, the
-program is ill-formed.
-[*Note 1*: The resolution of the address of an overload set in other
 contexts is described in [[over.over]]. — *end note*]
 ##### Call to named function <a id="over.call.func">[[over.call.func]]</a>
 Of interest in  [[over.call.func]] are only those function calls in
-which the *postfix-expression* ultimately contains a name that denotes
-one or more functions that might be called. Such a *postfix-expression*,
-perhaps nested arbitrarily deep in parentheses, has one of the following
-forms:
 ``` bnf
 postfix-expression:
     postfix-expression '.' id-expression
     postfix-expression '->' id-expression
@@ -169,52 +205,94 @@ postfix-expression:
 ```
 These represent two syntactic subcategories of function calls: qualified
 function calls and unqualified function calls.
-In qualified function calls, the name to be resolved is an
-*id-expression* and is preceded by an `->` or `.` operator. Since the
-construct `A->B` is generally equivalent to `(*A).B`, the rest of
-[[over]] assumes, without loss of generality, that all member function
-calls have been normalized to the form that uses an object and the `.`
-operator. Furthermore, [[over]] assumes that the *postfix-expression*
-that is the left operand of the `.` operator has type “cv `T`” where `T`
-denotes a class.[^3] Under this assumption, the *id-expression* in the
-call is looked up as a member function of `T` following the rules for
-looking up names in classes [[class.member.lookup]]. The function
-declarations found by that lookup constitute the set of candidate
-functions. The argument list is the *expression-list* in the call
-augmented by the addition of the left operand of the `.` operator in the
-normalized member function call as the implied object argument
-[[over.match.funcs]].
-In unqualified function calls, the name is not qualified by an `->` or
-`.` operator and has the more general form of a *primary-expression*.
-The name is looked up in the context of the function call following the
-normal rules for name lookup in expressions [[basic.lookup]]. The
-function declarations found by that lookup constitute the set of
-candidate functions. Because of the rules for name lookup, the set of
-candidate functions consists (1) entirely of non-member functions or (2)
-entirely of member functions of some class `T`. In case (1), the
-argument list is the same as the *expression-list* in the call. In case
-(2), the argument list is the *expression-list* in the call augmented by
-the addition of an implied object argument as in a qualified function
-call. If the keyword `this` [[class.this]] is in scope and refers to
-class `T`, or a derived class of `T`, then the implied object argument
-is `(*this)`. If the keyword `this` is not in scope or refers to another
-class, then a contrived object of type `T` becomes the implied object
-argument.[^4] If the argument list is augmented by a contrived object
-and overload resolution selects one of the non-static member functions
-of `T`, the call is ill-formed.
 ##### Call to object of class type <a id="over.call.object">[[over.call.object]]</a>
 If the *postfix-expression* `E` in the function call syntax evaluates to
 a class object of type “cv `T`”, then the set of candidate functions
 includes at least the function call operators of `T`. The function call
-operators of `T` are obtained by ordinary lookup of the name
-`operator()` in the context of `(E).operator()`.
 In addition, for each non-explicit conversion function declared in `T`
 of the form
 ``` bnf
@@ -236,27 +314,23 @@ returning `R`”, a *surrogate call function* with the unique name
 is also considered as a candidate function. Similarly, surrogate call
 functions are added to the set of candidate functions for each
 non-explicit conversion function declared in a base class of `T`
 provided the function is not hidden within `T` by another intervening
-declaration.[^5]
 The argument list submitted to overload resolution consists of the
 argument expressions present in the function call syntax preceded by the
 implied object argument `(E)`.
-[*Note 2*: When comparing the call against the function call operators,
-the implied object argument is compared against the implicit object
-parameter of the function call operator. When comparing the call against
-a surrogate call function, the implied object argument is compared
-against the first parameter of the surrogate call function. The
-conversion function from which the surrogate call function was derived
-will be used in the conversion sequence for that parameter since it
-converts the implied object argument to the appropriate function pointer
-or reference required by that first parameter. — *end note*]
-[*Example 1*:
 ``` cpp
 int f1(int);
 int f2(float);
 typedef int (*fp1)(int);
@@ -302,11 +376,11 @@ void f() {
 ```
 — *end example*]
 If either operand has a type that is a class or an enumeration, a
-user-defined operator function might be declared that implements this
 operator or a user-defined conversion can be necessary to convert the
 operand to a type that is appropriate for a built-in operator. In this
 case, overload resolution is used to determine which operator function
 or built-in operator is to be invoked to implement the operator.
 Therefore, the operator notation is first transformed to the equivalent
@@ -332,21 +406,21 @@ binary operator `@` with a left operand of type *cv1* `T1` and a right
 operand of type *cv2* `T2`, four sets of candidate functions, designated
 *member candidates*, *non-member candidates*, *built-in candidates*, and
 *rewritten candidates*, are constructed as follows:
 - If `T1` is a complete class type or a class currently being defined,
-  the set of member candidates is the result of the qualified lookup of
-  `T1::operator@` [[over.call.func]]; otherwise, the set of member
- candidates is empty.
-- The set of non-member candidates is the result of the unqualified
- lookup of `operator@` in the context of the expression according to
- the usual rules for name lookup in unqualified function calls
-  [[basic.lookup.argdep]] except that all member functions are ignored.
-  However, if no operand has a class type, only those non-member
-  functions in the lookup set that have a first parameter of type `T1`
-  or “reference to cv `T1`”, when `T1` is an enumeration type, or (if
-  there is a right operand) a second parameter of type `T2` or
   “reference to cv `T2`”, when `T2` is an enumeration type, are
   candidate functions.
 - For the operator `,`, the unary operator `&`, or the operator `->`,
   the built-in candidates set is empty. For all other operators, the
   built-in candidates include all of the candidate operator functions
@@ -354,32 +428,76 @@ operand of type *cv2* `T2`, four sets of candidate functions, designated
   - have the same operator name, and
   - accept the same number of operands, and
   - accept operand types to which the given operand or operands can be
     converted according to [[over.best.ics]], and
   - do not have the same parameter-type-list as any non-member candidate
-    that is not a function template specialization.
 - The rewritten candidate set is determined as follows:
   - For the relational [[expr.rel]] operators, the rewritten candidates
     include all non-rewritten candidates for the expression `x <=> y`.
   - For the relational [[expr.rel]] and three-way comparison
     [[expr.spaceship]] operators, the rewritten candidates also include
     a synthesized candidate, with the order of the two parameters
     reversed, for each non-rewritten candidate for the expression
     `y <=> x`.
   - For the `!=` operator [[expr.eq]], the rewritten candidates include
-    all non-rewritten candidates for the expression `x == y`.
   - For the equality operators, the rewritten candidates also include a
     synthesized candidate, with the order of the two parameters
     reversed, for each non-rewritten candidate for the expression
-    `y == x`.
   - For all other operators, the rewritten candidate set is empty.
   \[*Note 2*: A candidate synthesized from a member candidate has its
- implicit object parameter as the second parameter, thus implicit
- conversions are considered for the first, but not for the second,
   parameter. — *end note*]
 For the built-in assignment operators, conversions of the left operand
 are restricted as follows:
 - no temporaries are introduced to hold the left operand, and
 - no user-defined conversions are applied to the left operand to achieve
@@ -392,13 +510,13 @@ The set of candidate functions for overload resolution for some operator
 the built-in candidates, and the rewritten candidates for that operator
 `@`.
 The argument list contains all of the operands of the operator. The best
 function from the set of candidate functions is selected according to
-[[over.match.viable]] and  [[over.match.best]].[^6]
-[*Example 2*:
 ``` cpp
 struct A {
   operator int();
 };
@@ -436,11 +554,11 @@ of the selected operation function, except that the second standard
 conversion sequence of a user-defined conversion sequence
 [[over.ics.user]] is not applied. Then the operator is treated as the
 corresponding built-in operator and interpreted according to
 [[expr.compound]].
-[*Example 3*:
 ``` cpp
 struct X {
   operator double();
 };
@@ -456,11 +574,11 @@ int *b = Y() + X();             // error: pointer arithmetic requires integral o
 — *end example*]
 The second operand of operator `->` is ignored in selecting an
 `operator->` function, and is not an argument when the `operator->`
 function is called. When `operator->` returns, the operator `->` is
-applied to the value returned, with the original second operand.[^7]
 If the operator is the operator `,`, the unary operator `&`, or the
 operator `->`, and there are no viable functions, then the operator is
 assumed to be the built-in operator and interpreted according to
 [[expr.compound]].
@@ -482,11 +600,11 @@ struct B {
 A a;
 void B::f() {
   operator+ (a,a);              // error: global operator hidden by member
-  a + a;                        // OK: calls global operator+
 }
 ```
 — *end note*]
@@ -520,90 +638,75 @@ Assuming that “*cv1* `T`” is the type of the object being initialized,
 with `T` a class type, the candidate functions are selected as follows:
 - The converting constructors [[class.conv.ctor]] of `T` are candidate
   functions.
 - When the type of the initializer expression is a class type “cv `S`”,
- the non-explicit conversion functions of `S` and its base classes are
- considered. When initializing a temporary object [[class.mem]] to be
- bound to the first parameter of a constructor where the parameter is
- of type “reference to *cv2* `T`” and the constructor is called with a
- single argument in the context of direct-initialization of an object
- of type “*cv3* `T`”, explicit conversion functions are also
- considered. Those that are not hidden within `S` and yield a type
- whose cv-unqualified version is the same type as `T` or is a derived
-  class thereof are candidate functions. A call to a conversion function
-  returning “reference to `X`” is a glvalue of type `X`, and such a
-  conversion function is therefore considered to yield `X` for this
-  process of selecting candidate functions.
 In both cases, the argument list has one argument, which is the
 initializer expression.
 [*Note 2*: This argument will be compared against the first parameter
-of the constructors and against the implicit object parameter of the
-conversion functions. — *end note*]
 #### Initialization by conversion function <a id="over.match.conv">[[over.match.conv]]</a>
 Under the conditions specified in  [[dcl.init]], as part of an
 initialization of an object of non-class type, a conversion function can
 be invoked to convert an initializer expression of class type to the
 type of the object being initialized. Overload resolution is used to
-select the conversion function to be invoked. Assuming that “*cv1* `T`”
-is the type of the object being initialized, and “cv `S`” is the type of
-the initializer expression, with `S` a class type, the candidate
-functions are selected as follows:
-- The conversion functions of `S` and its base classes are considered.
- Those non-explicit conversion functions that are not hidden within `S`
- and yield type `T` or a type that can be converted to type `T` via a
- standard conversion sequence [[over.ics.scs]] are candidate functions.
- For direct-initialization, those explicit conversion functions that
- are not hidden within `S` and yield type `T` or a type that can be
-  converted to type `T` with a qualification conversion [[conv.qual]]
-  are also candidate functions. Conversion functions that return a
-  cv-qualified type are considered to yield the cv-unqualified version
-  of that type for this process of selecting candidate functions. A call
-  to a conversion function returning “reference to `X`” is a glvalue of
-  type `X`, and such a conversion function is therefore considered to
-  yield `X` for this process of selecting candidate functions.
 The argument list has one argument, which is the initializer expression.
-[*Note 1*: This argument will be compared against the implicit object
-parameter of the conversion functions. — *end note*]
 #### Initialization by conversion function for direct reference binding <a id="over.match.ref">[[over.match.ref]]</a>
 Under the conditions specified in  [[dcl.init.ref]], a reference can be
 bound directly to the result of applying a conversion function to an
 initializer expression. Overload resolution is used to select the
 conversion function to be invoked. Assuming that “reference to *cv1*
-`T`” is the type of the reference being initialized, and “cv `S`” is the
-type of the initializer expression, with `S` a class type, the candidate
 functions are selected as follows:
-- The conversion functions of `S` and its base classes are considered.
- Those non-explicit conversion functions that are not hidden within `S`
-  and yield type “lvalue reference to *cv2* `T2`” (when initializing an
- lvalue reference or an rvalue reference to function) or “*cv2* `T2`”
-  or “rvalue reference to *cv2* `T2`” (when initializing an rvalue
-  reference or an lvalue reference to function), where “*cv1* `T`” is
- reference-compatible [[dcl.init.ref]] with “*cv2* `T2`”, are candidate
-  functions. For direct-initialization, those explicit conversion
- functions that are not hidden within `S` and yield type “lvalue
- reference to *cv2* `T2`” (when initializing an lvalue reference or an
- rvalue reference to function) or “rvalue reference to *cv2* `T2`”
- (when initializing an rvalue reference or an lvalue reference to
- function), where `T2` is the same type as `T` or can be converted to
-  type `T` with a qualification conversion [[conv.qual]], are also
-  candidate functions.
 The argument list has one argument, which is the initializer expression.
-[*Note 1*: This argument will be compared against the implicit object
-parameter of the conversion functions. — *end note*]
 #### Initialization by list-initialization <a id="over.match.list">[[over.match.list]]</a>
 When objects of non-aggregate class type `T` are list-initialized such
 that [[dcl.init.list]] specifies that overload resolution is performed
@@ -622,15 +725,15 @@ resolution selects the constructor in two phases:
   consists of the elements of the initializer list.
 In copy-list-initialization, if an explicit constructor is chosen, the
 initialization is ill-formed.
-[*Note 1*: This differs from other situations ([[over.match.ctor]],
-[[over.match.copy]]), where only converting constructors are considered
-for copy-initialization. This restriction only applies if this
-initialization is part of the final result of overload
-resolution. — *end note*]
 #### Class template argument deduction <a id="over.match.class.deduct">[[over.match.class.deduct]]</a>
 When resolving a placeholder for a deduced class type
 [[dcl.type.class.deduct]] where the *template-name* names a primary
@@ -669,35 +772,112 @@ the elements of the *initializer-list* or *designated-initializer-list*
 of the *braced-init-list*, or of the *expression-list*. For each xᵢ, let
 eᵢ be the corresponding aggregate element of `C` or of one of its
 (possibly recursive) subaggregates that would be initialized by xᵢ
 [[dcl.init.aggr]] if
-- brace elision is not considered for any aggregate element that has a
-  dependent non-array type or an array type with a value-dependent
-  bound, and
 - each non-trailing aggregate element that is a pack expansion is
   assumed to correspond to no elements of the initializer list, and
 - a trailing aggregate element that is a pack expansion is assumed to
   correspond to all remaining elements of the initializer list (if any).
 If there is no such aggregate element eᵢ for any xᵢ, the aggregate
 deduction candidate is not added to the set. The aggregate deduction
 candidate is derived as above from a hypothetical constructor
 `C`(`T₁`, …, `Tₙ`), where
-- if eᵢ is of array type and xᵢ is a *braced-init-list* or
- *string-literal*, `Tᵢ` is an rvalue reference to the declared type of
- eᵢ, and
 - otherwise, `Tᵢ` is the declared type of eᵢ,
 except that additional parameter packs of the form `Pⱼ` `...` are
 inserted into the parameter list in their original aggregate element
 position corresponding to each non-trailing aggregate element of type
 `Pⱼ` that was skipped because it was a parameter pack, and the trailing
 sequence of parameters corresponding to a trailing aggregate element
 that is a pack expansion (if any) is replaced by a single parameter of
-the form `Tₙ` `...`.
 When resolving a placeholder for a deduced class type
 [[dcl.type.simple]] where the *template-name* names an alias template
 `A`, the *defining-type-id* of `A` must be of the form
@@ -709,14 +889,16 @@ as specified in [[dcl.type.simple]]. The guides of `A` are the set of
 functions or function templates formed as follows. For each function or
 function template `f` in the guides of the template named by the
 *simple-template-id* of the *defining-type-id*, the template arguments
 of the return type of `f` are deduced from the *defining-type-id* of `A`
 according to the process in [[temp.deduct.type]] with the exception that
-deduction does not fail if not all template arguments are deduced. Let
-`g` denote the result of substituting these deductions into `f`. If
-substitution succeeds, form a function or function template `f'` with
-the following properties and add it to the set of guides of `A`:
 - The function type of `f'` is the function type of `g`.
 - If `f` is a function template, `f'` is a function template whose
   template parameter list consists of all the template parameters of `A`
   (including their default template arguments) that appear in the above
@@ -726,14 +908,14 @@ the following properties and add it to the set of guides of `A`:
   function template.
 - The associated constraints [[temp.constr.decl]] are the conjunction of
   the associated constraints of `g` and a constraint that is satisfied
   if and only if the arguments of `A` are deducible (see below) from the
   return type.
-- If `f` is a copy deduction candidate [[over.match.class.deduct]], then
- `f'` is considered to be so as well.
-- If `f` was generated from a *deduction-guide*
- [[over.match.class.deduct]], then `f'` is considered to be so as well.
 - The *explicit-specifier* of `f'` is the *explicit-specifier* of `g`
   (if any).
 The arguments of a template `A` are said to be deducible from a type `T`
 if, given a class template
@@ -771,11 +953,11 @@ If the function or function template was generated from a constructor or
 *deduction-guide* that had an *explicit-specifier*, each such notional
 constructor is considered to have that same *explicit-specifier*. All
 such notional constructors are considered to be public members of the
 hypothetical class type.
-[*Example 1*:
 ``` cpp
 template <class T> struct A {
   explicit A(const T&, ...) noexcept;               // #1
   A(T&&, ...);                                      // #2
@@ -853,11 +1035,11 @@ F f2 = {Types<X, Y, Z>{}, X{}, Y{}};    // OK, F<X, Y, Z> deduced
 F f3 = {Types<X, Y, Z>{}, X{}, W{}};    // error: conflicting types deduced; operator Y not considered
 ```
 — *end example*]
-[*Example 2*:
 ``` cpp
 template <class T, class U> struct C {
   C(T, U);                                      // #1
 };
@@ -884,11 +1066,11 @@ Possible exposition-only implementation of the above procedure:
 template <class> class AA;
 template <class V> class AA<A<V>> { };
 template <class T> concept deduces_A = requires { sizeof(AA<T>); };
 // f1 is formed from the constructor #1 of C, generating the following function template
-template<T, U>
   auto f1(T, U) -> C<T, U>;
 // Deducing arguments for C<T, U> from C<V *, V*> deduces T as V * and U as V *;
 // f1' is obtained by transforming f1 as described by the above procedure.
 template<class V> requires deduces_A<C<V *, V *>>

 ### Candidate functions and argument lists <a id="over.match.funcs">[[over.match.funcs]]</a>
+#### General <a id="over.match.funcs.general">[[over.match.funcs.general]]</a>
 The subclauses of  [[over.match.funcs]] describe the set of candidate
 functions and the argument list submitted to overload resolution in each
 context in which overload resolution is used. The source transformations
 and constructions defined in these subclauses are only for the purpose
 of describing the overload resolution process. An implementation is not
 required to use such transformations and constructions.
 The set of candidate functions can contain both member and non-member
+functions to be resolved against the same argument list. If a member
+function is
+- an implicit object member function that is not a constructor, or
+- a static member function and the argument list includes an implied
+  object argument,
+it is considered to have an extra first parameter, called the
+*implicit object parameter*, which represents the object for which the
+member function has been called.
 Similarly, when appropriate, the context can construct an argument list
 that contains an *implied object argument* as the first argument in the
 list to denote the object to be operated on.
+For implicit object member functions, the type of the implicit object
 parameter is
 - “lvalue reference to cv `X`” for functions declared without a
   *ref-qualifier* or with the `&` *ref-qualifier*
 - “rvalue reference to cv `X`” for functions declared with the `&&`
 where `X` is the class of which the function is a member and cv is the
 cv-qualification on the member function declaration.
 [*Example 1*: For a `const` member function of class `X`, the extra
+parameter is assumed to have type “lvalue reference to
 `const X`”. — *end example*]
+For conversion functions that are implicit object member functions, the
+function is considered to be a member of the class of the implied object
+argument for the purpose of defining the type of the implicit object
+parameter. For non-conversion functions that are implicit object member
+functions nominated by a *using-declaration* in a derived class, the
+function is considered to be a member of the derived class for the
+purpose of defining the type of the implicit object parameter. For
+static member functions, the implicit object parameter is considered to
+match any object (since if the function is selected, the object is
+discarded).
 [*Note 1*: No actual type is established for the implicit object
 parameter of a static member function, and no attempt will be made to
 determine a conversion sequence for that parameter
 [[over.match.best]]. — *end note*]
 During overload resolution, the implied object argument is
 indistinguishable from other arguments. The implicit object parameter,
 however, retains its identity since no user-defined conversions can be
+applied to achieve a type match with it. For implicit object member
+functions declared without a *ref-qualifier*, even if the implicit
+object parameter is not const-qualified, an rvalue can be bound to the
 parameter as long as in all other respects the argument can be converted
 to the type of the implicit object parameter.
 [*Note 2*: The fact that such an argument is an rvalue does not affect
 the ranking of implicit conversion sequences
 [[over.ics.rank]]. — *end note*]
 Because other than in list-initialization only one user-defined
 conversion is allowed in an implicit conversion sequence, special rules
+apply when selecting the best user-defined conversion
+[[over.match.best]], [[over.best.ics]].
 [*Example 2*:
 ``` cpp
 class T {
 T a = 1;            // error: no viable conversion (T(C(1)) not considered)
 ```
 — *end example*]
+In each case where conversion functions of a class `S` are considered
+for initializing an object or reference of type `T`, the candidate
+functions include the result of a search for the
+*conversion-function-id* `operator T` in `S`.
+[*Note 3*: This search can find a specialization of a conversion
+function template [[basic.lookup]]. — *end note*]
+Each such case also defines sets of *permissible types* for explicit and
+non-explicit conversion functions; each (non-template) conversion
+function that
+- is a non-hidden member of `S`,
+- yields a permissible type, and,
+- for the former set, is non-explicit
+is also a candidate function. If initializing an object, for any
+permissible type cv `U`, any *cv2* `U`, *cv2* `U&`, or *cv2* `U&&` is
+also a permissible type. If the set of permissible types for explicit
+conversion functions is empty, any candidates that are explicit are
+discarded.
 In each case where a candidate is a function template, candidate
 function template specializations are generated using template argument
+deduction [[temp.over]], [[temp.deduct]]. If a constructor template or
+conversion function template has an *explicit-specifier* whose
 *constant-expression* is value-dependent [[temp.dep]], template argument
+deduction is performed first and then, if the context admits only
+candidates that are not explicit and the generated specialization is
 explicit [[dcl.fct.spec]], it will be removed from the candidate set.
 Those candidates are then handled as candidate functions in the usual
+way.[^1]
+A given name can refer to, or a conversion can consider, one or more
+function templates as well as a set of non-template functions. In such a
+case, the candidate functions generated from each function template are
+combined with the set of non-template candidate functions.
+A defaulted move special member function
+[[class.copy.ctor]], [[class.copy.assign]] that is defined as deleted is
+excluded from the set of candidate functions in all contexts. A
+constructor inherited from class type `C` [[class.inhctor.init]] that
+has a first parameter of type “reference to *cv1* `P`” (including such a
+constructor instantiated from a template) is excluded from the set of
+candidate functions when constructing an object of type *cv2* `D` if the
+argument list has exactly one argument and `C` is reference-related to
+`P` and `P` is reference-related to `D`.
 [*Example 3*:
 ``` cpp
 struct A {
 — *end example*]
 #### Function call syntax <a id="over.match.call">[[over.match.call]]</a>
+##### General <a id="over.match.call.general">[[over.match.call.general]]</a>
 In a function call [[expr.call]]
 ``` bnf
 postfix-expression '(' expression-listₒₚₜ ')'
 ```
 [[over.call.func]]. If the *postfix-expression* denotes an object of
 class type, overload resolution is applied as specified in
 [[over.call.object]].
 If the *postfix-expression* is the address of an overload set, overload
+resolution is applied using that set as described above.
+[*Note 1*: No implied object argument is added in this
+case. — *end note*]
+If the function selected by overload resolution is an implicit object
+member function, the program is ill-formed.
+[*Note 2*: The resolution of the address of an overload set in other
 contexts is described in [[over.over]]. — *end note*]
 ##### Call to named function <a id="over.call.func">[[over.call.func]]</a>
 Of interest in  [[over.call.func]] are only those function calls in
+which the *postfix-expression* ultimately contains an *id-expression*
+that denotes one or more functions. Such a *postfix-expression*, perhaps
+nested arbitrarily deep in parentheses, has one of the following forms:
 ``` bnf
 postfix-expression:
     postfix-expression '.' id-expression
     postfix-expression '->' id-expression
 ```
 These represent two syntactic subcategories of function calls: qualified
 function calls and unqualified function calls.
+In qualified function calls, the function is named by an *id-expression*
+preceded by an `->` or `.` operator. Since the construct `A->B` is
+generally equivalent to `(*A).B`, the rest of [[over]] assumes, without
+loss of generality, that all member function calls have been normalized
+to the form that uses an object and the `.` operator. Furthermore,
+[[over]] assumes that the *postfix-expression* that is the left operand
+of the `.` operator has type “cv `T`” where `T` denotes a class.[^2]
+The function declarations found by name lookup [[class.member.lookup]]
+constitute the set of candidate functions. The argument list is the
+*expression-list* in the call augmented by the addition of the left
+operand of the `.` operator in the normalized member function call as
+the implied object argument [[over.match.funcs]].
+In unqualified function calls, the function is named by a
+*primary-expression*. The function declarations found by name lookup
+[[basic.lookup]] constitute the set of candidate functions. Because of
+the rules for name lookup, the set of candidate functions consists
+either entirely of non-member functions or entirely of member functions
+of some class `T`. In the former case or if the *primary-expression* is
+the address of an overload set, the argument list is the same as the
+*expression-list* in the call. Otherwise, the argument list is the
+*expression-list* in the call augmented by the addition of an implied
+object argument as in a qualified function call. If the current class
+is, or is derived from, `T`, and the keyword `this` [[expr.prim.this]]
+refers to it, then the implied object argument is `(*this)`. Otherwise,
+a contrived object of type `T` becomes the implied object argument;[^3]
+if overload resolution selects a non-static member function, the call is
+ill-formed.
+[*Example 1*:
+``` cpp
+struct C {
+  void a();
+  void b() {
+    a();                // OK, (*this).a()
+  }
+void c(this const C&);      // #1
+void c()&;                  // #2
+static void c(int = 0);     // #3
+void d() {
+  c();                  // error: ambiguous between #2 and #3
+  (C::c)();             // error: as above
+  (&(C::c))();          // error: cannot resolve address of overloaded this->C::c[over.over]
+  (&C::c)(C{});         // selects #1
+  (&C::c)(*this);       // error: selects #2, and is ill-formed[over.match.call.general]
+  (&C::c)();            // selects #3
+}
+  void f(this const C&);
+  void g() const {
+    f();                // OK, (*this).f()
+    f(*this);           // error: no viable candidate for (*this).f(*this)
+    this->f();          // OK
+  }
+  static void h() {
+    f();                // error: contrived object argument, but overload resolution
+                        // picked a non-static member function
+    f(C{});             // error: no viable candidate
+    C{}.f();            // OK
+  }
+  void k(this int);
+  operator int() const;
+  void m(this const C& c) {
+    c.k();              // OK
+  }
+};
+```
+— *end example*]
 ##### Call to object of class type <a id="over.call.object">[[over.call.object]]</a>
 If the *postfix-expression* `E` in the function call syntax evaluates to
 a class object of type “cv `T`”, then the set of candidate functions
 includes at least the function call operators of `T`. The function call
+operators of `T` are the results of a search for the name `operator()`
+in the scope of `T`.
 In addition, for each non-explicit conversion function declared in `T`
 of the form
 ``` bnf
 is also considered as a candidate function. Similarly, surrogate call
 functions are added to the set of candidate functions for each
 non-explicit conversion function declared in a base class of `T`
 provided the function is not hidden within `T` by another intervening
+declaration.[^4]
 The argument list submitted to overload resolution consists of the
 argument expressions present in the function call syntax preceded by the
 implied object argument `(E)`.
+[*Note 3*: When comparing the call against the function call operators,
+the implied object argument is compared against the object parameter of
+the function call operator. When comparing the call against a surrogate
+call function, the implied object argument is compared against the first
+parameter of the surrogate call function. — *end note*]
+[*Example 2*:
 ``` cpp
 int f1(int);
 int f2(float);
 typedef int (*fp1)(int);
 ```
 — *end example*]
 If either operand has a type that is a class or an enumeration, a
+user-defined operator function can be declared that implements this
 operator or a user-defined conversion can be necessary to convert the
 operand to a type that is appropriate for a built-in operator. In this
 case, overload resolution is used to determine which operator function
 or built-in operator is to be invoked to implement the operator.
 Therefore, the operator notation is first transformed to the equivalent
 operand of type *cv2* `T2`, four sets of candidate functions, designated
 *member candidates*, *non-member candidates*, *built-in candidates*, and
 *rewritten candidates*, are constructed as follows:
 - If `T1` is a complete class type or a class currently being defined,
+  the set of member candidates is the result of a search for `operator@`
+ in the scope of `T1`; otherwise, the set of member candidates is
+  empty.
+- For the operators `=`, `[]`, or `->`, the set of non-member candidates
+ is empty; otherwise, it includes the result of unqualified lookup for
+ `operator@` in the rewritten function call
+  [[basic.lookup.unqual]], [[basic.lookup.argdep]], ignoring all member
+ functions. However, if no operand has a class type, only those
+ non-member functions in the lookup set that have a first parameter of
+ type `T1` or “reference to cv `T1`”, when `T1` is an enumeration type,
+ or (if there is a right operand) a second parameter of type `T2` or
   “reference to cv `T2`”, when `T2` is an enumeration type, are
   candidate functions.
 - For the operator `,`, the unary operator `&`, or the operator `->`,
   the built-in candidates set is empty. For all other operators, the
   built-in candidates include all of the candidate operator functions
   - have the same operator name, and
   - accept the same number of operands, and
   - accept operand types to which the given operand or operands can be
     converted according to [[over.best.ics]], and
   - do not have the same parameter-type-list as any non-member candidate
+ or rewritten non-member candidate that is not a function template
+    specialization.
 - The rewritten candidate set is determined as follows:
   - For the relational [[expr.rel]] operators, the rewritten candidates
     include all non-rewritten candidates for the expression `x <=> y`.
   - For the relational [[expr.rel]] and three-way comparison
     [[expr.spaceship]] operators, the rewritten candidates also include
     a synthesized candidate, with the order of the two parameters
     reversed, for each non-rewritten candidate for the expression
     `y <=> x`.
   - For the `!=` operator [[expr.eq]], the rewritten candidates include
+    all non-rewritten candidates for the expression `x == y` that are
+    rewrite targets with first operand `x` (see below).
   - For the equality operators, the rewritten candidates also include a
     synthesized candidate, with the order of the two parameters
     reversed, for each non-rewritten candidate for the expression
+    `y == x` that is a rewrite target with first operand `y`.
   - For all other operators, the rewritten candidate set is empty.
   \[*Note 2*: A candidate synthesized from a member candidate has its
+  object parameter as the second parameter, thus implicit conversions
+  are considered for the first, but not for the second,
   parameter. — *end note*]
+A non-template function or function template `F` named `operator==` is a
+rewrite target with first operand `o` unless a search for the name
+`operator!=` in the scope S from the instantiation context of the
+operator expression finds a function or function template that would
+correspond [[basic.scope.scope]] to `F` if its name were `operator==`,
+where S is the scope of the class type of `o` if `F` is a class member,
+and the namespace scope of which `F` is a member otherwise. A function
+template specialization named `operator==` is a rewrite target if its
+function template is a rewrite target.
+[*Example 2*:
+``` cpp
+struct A {};
+template<typename T> bool operator==(A, T);     // #1
+bool a1 = 0 == A();                             // OK, calls reversed #1
+template<typename T> bool operator!=(A, T);
+bool a2 = 0 == A();                             // error, #1 is not a rewrite target
+struct B {
+  bool operator==(const B&);    // #2
+};
+struct C : B {
+  C();
+  C(B);
+  bool operator!=(const B&);    // #3
+};
+bool c1 = B() == C();           // OK, calls #2; reversed #2 is not a candidate
+                                // because search for operator!= in C finds #3
+bool c2 = C() == B();           // error: ambiguous between #2 found when searching C and
+                                // reversed #2 found when searching B
+struct D {};
+template<typename T> bool operator==(D, T);     // #4
+inline namespace N {
+  template<typename T> bool operator!=(D, T);   // #5
+}
+bool d1 = 0 == D();             // OK, calls reversed #4; #5 does not forbid #4 as a rewrite target
+```
+— *end example*]
 For the built-in assignment operators, conversions of the left operand
 are restricted as follows:
 - no temporaries are introduced to hold the left operand, and
 - no user-defined conversions are applied to the left operand to achieve
 the built-in candidates, and the rewritten candidates for that operator
 `@`.
 The argument list contains all of the operands of the operator. The best
 function from the set of candidate functions is selected according to
+[[over.match.viable]] and  [[over.match.best]].[^5]
+[*Example 3*:
 ``` cpp
 struct A {
   operator int();
 };
 conversion sequence of a user-defined conversion sequence
 [[over.ics.user]] is not applied. Then the operator is treated as the
 corresponding built-in operator and interpreted according to
 [[expr.compound]].
+[*Example 4*:
 ``` cpp
 struct X {
   operator double();
 };
 — *end example*]
 The second operand of operator `->` is ignored in selecting an
 `operator->` function, and is not an argument when the `operator->`
 function is called. When `operator->` returns, the operator `->` is
+applied to the value returned, with the original second operand.[^6]
 If the operator is the operator `,`, the unary operator `&`, or the
 operator `->`, and there are no viable functions, then the operator is
 assumed to be the built-in operator and interpreted according to
 [[expr.compound]].
 A a;
 void B::f() {
   operator+ (a,a);              // error: global operator hidden by member
+  a + a;                        // OK, calls global operator+
 }
 ```
 — *end note*]
 with `T` a class type, the candidate functions are selected as follows:
 - The converting constructors [[class.conv.ctor]] of `T` are candidate
   functions.
 - When the type of the initializer expression is a class type “cv `S`”,
+  conversion functions are considered. The permissible types for
+ non-explicit conversion functions are `T` and any class derived from
+ `T`. When initializing a temporary object [[class.mem]] to be bound to
+ the first parameter of a constructor where the parameter is of type
+ “reference to *cv2* `T`” and the constructor is called with a single
+ argument in the context of direct-initialization of an object of type
+ “*cv3* `T`”, the permissible types for explicit conversion functions
+ are the same; otherwise there are none.
 In both cases, the argument list has one argument, which is the
 initializer expression.
 [*Note 2*: This argument will be compared against the first parameter
+of the constructors and against the object parameter of the conversion
+functions. — *end note*]
 #### Initialization by conversion function <a id="over.match.conv">[[over.match.conv]]</a>
 Under the conditions specified in  [[dcl.init]], as part of an
 initialization of an object of non-class type, a conversion function can
 be invoked to convert an initializer expression of class type to the
 type of the object being initialized. Overload resolution is used to
+select the conversion function to be invoked. Assuming that “cv `T`” is
+the type of the object being initialized, the candidate functions are
+selected as follows:
+- The permissible types for non-explicit conversion functions are those
+ that can be converted to type `T` via a standard conversion sequence
+ [[over.ics.scs]]. For direct-initialization, the permissible types for
+ explicit conversion functions are those that can be converted to type
+ `T` with a (possibly trivial) qualification conversion [[conv.qual]];
+ otherwise there are none.
 The argument list has one argument, which is the initializer expression.
+[*Note 1*: This argument will be compared against the object parameter
+of the conversion functions. — *end note*]
 #### Initialization by conversion function for direct reference binding <a id="over.match.ref">[[over.match.ref]]</a>
 Under the conditions specified in  [[dcl.init.ref]], a reference can be
 bound directly to the result of applying a conversion function to an
 initializer expression. Overload resolution is used to select the
 conversion function to be invoked. Assuming that “reference to *cv1*
+`T`” is the type of the reference being initialized, the candidate
 functions are selected as follows:
+- Let R be a set of types including
+  - “lvalue reference to *cv2* `T2`” (when initializing an lvalue
+    reference or an rvalue reference to function) and
+ - “*cv2* `T2`” and “rvalue reference to *cv2* `T2`” (when initializing
+    an rvalue reference or an lvalue reference to function)
+ for any `T2`. The permissible types for non-explicit conversion
+  functions are the members of R where “*cv1* `T`” is
+ reference-compatible [[dcl.init.ref]] with “*cv2* `T2`”. For
+ direct-initialization, the permissible types for explicit conversion
+ functions are the members of R where `T2` can be converted to type `T`
+ with a (possibly trivial) qualification conversion [[conv.qual]];
+ otherwise there are none.
 The argument list has one argument, which is the initializer expression.
+[*Note 1*: This argument will be compared against the object parameter
+of the conversion functions. — *end note*]
 #### Initialization by list-initialization <a id="over.match.list">[[over.match.list]]</a>
 When objects of non-aggregate class type `T` are list-initialized such
 that [[dcl.init.list]] specifies that overload resolution is performed
   consists of the elements of the initializer list.
 In copy-list-initialization, if an explicit constructor is chosen, the
 initialization is ill-formed.
+[*Note 1*: This differs from other situations
+[[over.match.ctor]], [[over.match.copy]], where only converting
+constructors are considered for copy-initialization. This restriction
+only applies if this initialization is part of the final result of
+overload resolution. — *end note*]
 #### Class template argument deduction <a id="over.match.class.deduct">[[over.match.class.deduct]]</a>
 When resolving a placeholder for a deduced class type
 [[dcl.type.class.deduct]] where the *template-name* names a primary
 of the *braced-init-list*, or of the *expression-list*. For each xᵢ, let
 eᵢ be the corresponding aggregate element of `C` or of one of its
 (possibly recursive) subaggregates that would be initialized by xᵢ
 [[dcl.init.aggr]] if
+- brace elision is not considered for any aggregate element that has
+ - a dependent non-array type,
+ - an array type with a value-dependent bound, or
+  - an array type with a dependent array element type and xᵢ is a string
+    literal; and
 - each non-trailing aggregate element that is a pack expansion is
   assumed to correspond to no elements of the initializer list, and
 - a trailing aggregate element that is a pack expansion is assumed to
   correspond to all remaining elements of the initializer list (if any).
 If there is no such aggregate element eᵢ for any xᵢ, the aggregate
 deduction candidate is not added to the set. The aggregate deduction
 candidate is derived as above from a hypothetical constructor
 `C`(`T₁`, …, `Tₙ`), where
+- if eᵢ is of array type and xᵢ is a *braced-init-list*, `Tᵢ` is an
+  rvalue reference to the declared type of eᵢ, and
+- if eᵢ is of array type and xᵢ is a *string-literal*, `Tᵢ` is an lvalue
+  reference to the const-qualified declared type of eᵢ, and
 - otherwise, `Tᵢ` is the declared type of eᵢ,
 except that additional parameter packs of the form `Pⱼ` `...` are
 inserted into the parameter list in their original aggregate element
 position corresponding to each non-trailing aggregate element of type
 `Pⱼ` that was skipped because it was a parameter pack, and the trailing
 sequence of parameters corresponding to a trailing aggregate element
 that is a pack expansion (if any) is replaced by a single parameter of
+the form `Tₙ` `...`. In addition, if `C` is defined and inherits
+constructors [[namespace.udecl]] from a direct base class denoted in the
+*base-specifier-list* by a *class-or-decltype* `B`, let `A` be an alias
+template whose template parameter list is that of `C` and whose
+*defining-type-id* is `B`. If `A` is a deducible template
+[[dcl.type.simple]], the set contains the guides of `A` with the return
+type `R` of each guide replaced with `typename CC<R>::type` given a
+class template
+``` cpp
+template <typename> class CC;
+```
+whose primary template is not defined and with a single partial
+specialization whose template parameter list is that of `A` and whose
+template argument list is a specialization of `A` with the template
+argument list of `A` [[temp.dep.type]] having a member typedef `type`
+designating a template specialization with the template argument list of
+`A` but with `C` as the template.
+[*Note 1*: Equivalently, the template parameter list of the
+specialization is that of `C`, the template argument list of the
+specialization is `B`, and the member typedef names `C` with the
+template argument list of `C`. — *end note*]
+[*Example 1*:
+``` cpp
+template <typename T> struct B {
+  B(T);
+};
+template <typename T> struct C : public B<T> {
+  using B<T>::B;
+};
+template <typename T> struct D : public B<T> {};
+C c(42);            // OK, deduces C<int>
+D d(42);            // error: deduction failed, no inherited deduction guides
+B(int) -> B<char>;
+C c2(42);           // OK, deduces C<char>
+template <typename T> struct E : public B<int> {
+  using B<int>::B;
+};
+E e(42);            // error: deduction failed, arguments of E cannot be deduced from introduced guides
+template <typename T, typename U, typename V> struct F {
+  F(T, U, V);
+};
+template <typename T, typename U> struct G : F<U, T, int> {
+  using G::F::F;
+}
+G g(true, 'a', 1);  // OK, deduces G<char, bool>
+template<class T, std::size_t N>
+struct H {
+  T array[N];
+};
+template<class T, std::size_t N>
+struct I {
+  volatile T array[N];
+};
+template<std::size_t N>
+struct J {
+  unsigned char array[N];
+};
+H h = { "abc" };    // OK, deduces H<char, 4> (not T = const char)
+I i = { "def" };    // OK, deduces I<char, 4>
+J j = { "ghi" };    // error: cannot bind reference to array of unsigned char to array of char in deduction
+```
+— *end example*]
 When resolving a placeholder for a deduced class type
 [[dcl.type.simple]] where the *template-name* names an alias template
 `A`, the *defining-type-id* of `A` must be of the form
 functions or function templates formed as follows. For each function or
 function template `f` in the guides of the template named by the
 *simple-template-id* of the *defining-type-id*, the template arguments
 of the return type of `f` are deduced from the *defining-type-id* of `A`
 according to the process in [[temp.deduct.type]] with the exception that
+deduction does not fail if not all template arguments are deduced. If
+deduction fails for another reason, proceed with an empty set of deduced
+template arguments. Let `g` denote the result of substituting these
+deductions into `f`. If substitution succeeds, form a function or
+function template `f'` with the following properties and add it to the
+set of guides of `A`:
 - The function type of `f'` is the function type of `g`.
 - If `f` is a function template, `f'` is a function template whose
   template parameter list consists of all the template parameters of `A`
   (including their default template arguments) that appear in the above
   function template.
 - The associated constraints [[temp.constr.decl]] are the conjunction of
   the associated constraints of `g` and a constraint that is satisfied
   if and only if the arguments of `A` are deducible (see below) from the
   return type.
+- If `f` is a copy deduction candidate, then `f'` is considered to be so
+  as well.
+- If `f` was generated from a *deduction-guide* [[temp.deduct.guide]],
+  then `f'` is considered to be so as well.
 - The *explicit-specifier* of `f'` is the *explicit-specifier* of `g`
   (if any).
 The arguments of a template `A` are said to be deducible from a type `T`
 if, given a class template
 *deduction-guide* that had an *explicit-specifier*, each such notional
 constructor is considered to have that same *explicit-specifier*. All
 such notional constructors are considered to be public members of the
 hypothetical class type.
+[*Example 2*:
 ``` cpp
 template <class T> struct A {
   explicit A(const T&, ...) noexcept;               // #1
   A(T&&, ...);                                      // #2
 F f3 = {Types<X, Y, Z>{}, X{}, W{}};    // error: conflicting types deduced; operator Y not considered
 ```
 — *end example*]
+[*Example 3*:
 ``` cpp
 template <class T, class U> struct C {
   C(T, U);                                      // #1
 };
 template <class> class AA;
 template <class V> class AA<A<V>> { };
 template <class T> concept deduces_A = requires { sizeof(AA<T>); };
 // f1 is formed from the constructor #1 of C, generating the following function template
+template<class T, class U>
   auto f1(T, U) -> C<T, U>;
 // Deducing arguments for C<T, U> from C<V *, V*> deduces T as V * and U as V *;
 // f1' is obtained by transforming f1 as described by the above procedure.
 template<class V> requires deduces_A<C<V *, V *>>

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