1517. default_delete's default constructor should be trivial

Section: 23.11.1.1.2 [unique.ptr.dltr.dflt] Status: C++11 Submitter: Daniel Krügler Opened: 2010-09-12 Last modified: 2016-02-10

Priority: Not Prioritized

View all other issues in [unique.ptr.dltr.dflt].

View all issues with C++11 status.

Discussion:

The current working draft does specify the default c'tor of default_delete in a manner to guarantee static initialization for default-constructed objects of static storage duration as a consequence of the acceptance of the proposal n2976 but this paper overlooked the fact that the suggested declaration does not ensure that the type will be a trivial type. The type default_delete was always considered as a simple wrapper for calling delete or delete[], respectivly and should be a trivial type.

In agreement with the new settled core language rules this easy to realize by just changing the declaration to

constexpr default_delete() = default;

This proposal also automatically solves the problem, that the semantics of the default constructor of the partial specialization default_delete<T[]> is not specified at all. By defaulting its default constructor as well, the semantics are well-defined.

[ Post-Rapperswil ]

Moved to Tentatively Ready after 5 positive votes on c++std-lib.

[ Adopted at 2010-11 Batavia ]

Proposed resolution:

The following wording changes are against N3126.

  1. Change the synopsis of the primary template definition of default_delete in [unique.ptr.dltr.dflt] as indicated:
    namespace std {
      template <class T> struct default_delete {
        constexpr default_delete() = default;
        template <class U> default_delete(const default_delete<U>&);
        void operator()(T*) const;
      };
    }
    
  2. Remove the prototype specification of the default_delete default constructor in [unique.ptr.dltr.dflt]/1. This brings it in harmony with the style used in the partial specialization default_delete<T[]>. Since there are neither implied nor explicit members, there is no possibility to misinterpret what the constructor does:
    constexpr default_delete();
    

    1 Effects: Default constructs a default_delete object.

  3. Change the synopsis of the partial specialization of default_delete in [unique.ptr.dltr.dflt1] as indicated:
    namespace std {
      template <class T> struct default_delete<T[]> {
        constexpr default_delete() = default;
        void operator()(T*) const;
        template <class U> void operator()(U*) const = delete;
      };
    }