This wording is relative to N4910.

[Drafting note: The below presented wording adds back the const T& constructor and its specification that were present before P2418R2. Furthermore it adds an additional constraint to the T&& constructor and simplifies the Effects of this constructors to the handle construction case.]

1. Modify [format.arg] as indicated:

   namespace std {
     template<class Context>
     class basic_format_arg {
     public:
       class handle;
   
     private:
       […]
       template<class T> explicit basic_format_arg(T&& v) noexcept; // exposition only
       template<class T> explicit basic_format_arg(const T& v) noexcept; // exposition only
       […]
     };
   }
   

   […]

   template<class T> explicit basic_format_arg(T&& v) noexcept;
   

   -4- Constraints: The template specialization

   typename Context::template formatter_type<remove_cvref_t<T>>
   

   meets the BasicFormatter requirements ([formatter.requirements]). The extent to which an implementation determines that the specialization meets the BasicFormatter requirements is unspecified, except that as a minimum the expression

   typename Context::template formatter_type<remove_cvref_t<T>>()
     .format(declval<T&>(), declval<Context&>())
   

   shall be well-formed when treated as an unevaluated operand ([expr.context]), and if this overload were not declared, the overload resolution would find no usable candidate or be ambiguous. [Note ?: This overload has no effect if the overload resolution among other overloads succeeds. — end note].

   -5- Effects:

   1. (5.1) — if T is bool or char_type, initializes value with v;

   2. (5.2) — otherwise, if T is char and char_type is wchar_t, initializes value with static_cast<wchar_t>(v);

   3. (5.3) — otherwise, if T is a signed integer type ([basic.fundamental]) and sizeof(T) <= sizeof(int), initializes value with static_cast<int>(v);

   4. (5.4) — otherwise, if T is an unsigned integer type and sizeof(T) <= sizeof(unsigned int), initializes value with static_cast<unsigned int>(v);

   5. (5.5) — otherwise, if T is a signed integer type and sizeof(T) <= sizeof(long long int), initializes value with static_cast<long long int>(v);

   6. (5.6) — otherwise, if T is an unsigned integer type and sizeof(T) <= sizeof(unsigned long long int), initializes value with static_cast<unsigned long long int>(v);

   7. (5.7) — otherwise, iInitializes value with handle(v).

   template<class T> explicit basic_format_arg(const T& v) noexcept;
   

   -?- Constraints: The template specialization

   typename Context::template formatter_type<T>
   

   meets the Formatter requirements ([formatter.requirements]). The extent to which an implementation determines that the specialization meets the Formatter requirements is unspecified, except that as a minimum the expression

   typename Context::template formatter_type<T>()
     .format(declval<const T&>(), declval<Context&>())
   

   shall be well-formed when treated as an unevaluated operand ([expr.context]).

   -?- Effects:

   1. (?.1) — if T is bool or char_type, initializes value with v;

   2. (?.2) — otherwise, if T is char and char_type is wchar_t, initializes value with static_cast<wchar_t>(v);

   3. (?.3) — otherwise, if T is a signed integer type ([basic.fundamental]) and sizeof(T) <= sizeof(int), initializes value with static_cast<int>(v);

   4. (?.4) — otherwise, if T is an unsigned integer type and sizeof(T) <= sizeof(unsigned int), initializes value with static_cast<unsigned int>(v);

   5. (?.5) — otherwise, if T is a signed integer type and sizeof(T) <= sizeof(long long int), initializes value with static_cast<long long int>(v);

   6. (?.6) — otherwise, if T is an unsigned integer type and sizeof(T) <= sizeof(unsigned long long int), initializes value with static_cast<unsigned long long int>(v);

   7. (?.7) — otherwise, initializes value with handle(v).