Proposed resolution:

This wording is relative to N4835.

1. Change Table 52 — "Sign modifications" in [tab:meta.trans.sign] as indicated:

   Table 52 — Sign modifications [tab:meta.trans.sign]

   Template	Comments
   template <class T> struct make_signed;	If T names a (possibly cv-qualified) signed integer type ([basic.fundamental]) then the member typedef type names the type T; otherwise, if T names a (possibly cv-qualified) unsigned integer type then type names the corresponding signed integer type, with the same cv-qualifiers as T; otherwise, type names the signed integer type with smallest rank ([conv.rank]) for which sizeof(T) == sizeof(type), with the same cv-qualifiers as T. RequiresMandates: T shall beis an (possibly cv-qualified) integral type or enumeration type other than cv but not a bool type.
   template <class T> struct make_unsigned;	If T names a (possibly cv-qualified) unsigned integer type ([basic.fundamental]) then the member typedef type names the type T; otherwise, if T names a (possibly cv-qualified) signed integer type then type names the corresponding unsigned integer type, with the same cv-qualifiers as T; otherwise, type names the unsigned integer type with smallest rank ([conv.rank]) for which sizeof(T) == sizeof(type), with the same cv-qualifiers as T. RequiresMandates: T shall beis an (possibly cv-qualified) integral type or enumeration type other than cv but not a bool type.

2. Change [iterator.range] as indicated:

   template<class C> constexpr auto ssize(const C& c)
     -> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;
   

   -18- ReturnsEffects: Equivalent to:

   return static_cast<common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>>(c.size());
   

[ 2019-11-23 Issue Prioritization ]

Status to Tentatively Ready after five positive votes on the reflector.

[ 2019-11-18; Casey comments and improves wording ]

It would be better to provided the Mandates: guarantee in [tab:meta.trans.sign] instead of one special place where the make_signed template is used. The wording below attempts to realize that.

[ 2019-10-28; Tim provides improved wording ]

Previous resolution [SUPERSEDED]:

This wording is relative to N4835.

1. Modify [iterator.range] as indicated:

   template<class C> constexpr auto ssize(const C& c)
     -> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;
   

   -?- Mandates: decltype(c.size()) is an integral or enumeration type other than bool.

   -18- Returns:

   static_cast<common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>>(c.size())
   

[ 2019-11-16 Issue Prioritization ]

Priority to 3 after reflector discussion.

Previous resolution [SUPERSEDED]:

This wording is relative to N4830.

1. Modify [iterator.range] as indicated:

   template<class C> constexpr auto ssize(const C& c)
     -> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;
   

   -?- Mandates: decltype(c.size()) is a (possibly cv-qualified) integral or enumeration type but not a bool type.

   -18- Returns:

   static_cast<common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>>(c.size())
   

The overload of ssize specified in [iterator.range]/18 has no constraints, yet it specializes make_signed_t which has a precondition that its type parameter is an integral type or enumeration but not bool ([meta.trans.sign]). This precondition needs to be propagated to ssize as "Mandates [or Constraints]: decltype(c.size()) [meets the requirements for the type argument to make_signed]". "Mandates" seems to be more in line with LWG guidance since there are no traits nor concepts that observe ssize.