Issue 2247: Type traits and std::nullptr_t

Title: Type traits and std::nullptr_t
Status: c++14
Section: [meta.unary.cat]
Submitter: Joe Gottman

Created on 2013-03-15.00:00:00 last changed 123 months ago

Messages

Date: 2013-09-29.10:27:09

Proposed resolution:

This wording is relative to N3485.

Edit [meta.type.synop], header <type_traits> synopsis:

namespace std {
  […]
  // 20.9.4.1, primary type categories:
  template <class T> struct is_void;
  template <class T> struct is_null_pointer;
  template <class T> struct is_integral;
  template <class T> struct is_floating_point;
  […]
}

Edit Table 47 — "Primary type category predicates" as indicated:

Table 47 — Primary type category predicates
Template Condition Comments

…

template <class T> struct is_null_pointer; T is std::nullptr_t ([basic.fundamental])

…

Table 47 — Primary type category predicates
Template	Condition	Comments
`…`
`template <class T> struct is_null_pointer;`	`T` is `std::nullptr_t` ([basic.fundamental])
`…`

msg6498 (view)

Date: 2013-09-15.00:00:00

[ 2013-09-29, Chicago ]

Apply to the Working Paper

msg6401 (view)

Date: 2013-04-15.00:00:00

[ 2013-04-20, Bristol ]

Rename to is_null_pointer, move to Ready

Previous wording:

This wording is relative to N3485.
Edit [meta.type.synop], header <type_traits> synopsis:
namespace std {
  […]
  // 20.9.4.1, primary type categories:
  template <class T> struct is_void;
  template <class T> struct is_nullptr;
  template <class T> struct is_integral;
  template <class T> struct is_floating_point;
  […]
}
Edit Table 47 — "Primary type category predicates" as indicated:

Table 47 — Primary type category predicates
Template Condition Comments

…

template <class T> struct is_nullptr; T is std::nullptr_t ([basic.fundamental])

…

Table 47 — Primary type category predicates
Template	Condition	Comments
`…`
`template <class T> struct is_nullptr;`	`T` is `std::nullptr_t` ([basic.fundamental])
`…`

msg6400 (view)

Date: 2013-03-15.00:00:00

According to [meta.unary.cat], for every type T, exactly one of the primary type traits is true. So which is true for the type std::nullptr_t? By [lex.nullptr] std::nullptr_t is not a pointer type or a pointer-to-member type, so is_pointer, is_member_object_pointer and is_member_function_pointer can't be true for std::nullptr_t, and none of the other primary type traits seem to apply.

History
Date	User	Action	Args
2014-02-20 13:20:35	admin	set	status: wp -> c++14
2013-09-29 10:27:09	admin	set	messages: + msg6654
2013-09-29 10:27:09	admin	set	status: voting -> wp
2013-09-23 13:24:31	admin	set	status: ready -> voting
2013-04-20 08:17:49	admin	set	messages: + msg6498
2013-04-20 08:17:49	admin	set	status: new -> ready
2013-03-17 22:52:52	admin	set	messages: + msg6401
2013-03-15 00:00:00	admin	create