2401. std::function needs more noexcept

Section: 23.14.13.2 [func.wrap.func] Status: C++17 Submitter: Stephan T. Lavavej Opened: 2014-06-14 Last modified: 2017-07-30

Priority: 0

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Discussion:

There are two issues here:

  1. std::function's constructor from nullptr_t is marked as noexcept, but its assignment operator from nullptr_t isn't. This assignment can and should be marked as noexcept.

  2. std::function's comparisons with nullptr_t are marked as noexcept in two out of three places.

[2014-06-16 Rapperswil]

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Proposed resolution:

This wording is relative to N3936.

  1. Change 23.14 [function.objects] p2, header <functional> synopsis, as indicated:

    namespace std {
      […]
      // 20.9.11 polymorphic function wrappers:
      […]
      template<class R, class... ArgTypes>
      bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
      template<class R, class... ArgTypes>
      bool operator==(nullptr_t, const function<R(ArgTypes...)>&) noexcept;
      template<class R, class... ArgTypes>
      bool operator!=(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
      template<class R, class... ArgTypes>
      bool operator!=(nullptr_t, const function<R(ArgTypes...)>&) noexcept;
      […]
    }
    
  2. Change 23.14.13.2 [func.wrap.func], class template function synopsis, as indicated:

    […]
    // 20.9.11.2.1, construct/copy/destroy:
    […]
    function& operator=(nullptr_t) noexcept;
    […]
    
  3. Change 23.14.13.2.1 [func.wrap.func.con] before p16 as indicated:

    function& operator=(nullptr_t) noexcept;