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2365. Missingnoexcept inshared_ptr::shared_ptr(nullptr_t)

Section: 20.3.2.2[util.smartptr.shared]Status:C++17Submitter: Cassio NeriOpened: 2014-02-13Last modified: 2017-07-30

Priority:Not Prioritized

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Discussion:

The declaration and definition ofshared_ptr::shared_ptr(nullptr_t), given in 20.3.2.2[util.smartptr.shared], is

constexpr shared_ptr(nullptr_t) : shared_ptr() { }

The intention seems clear: this constructor should have the same semantics of the default constructor. However, contrarily to the default constructor, this one is notnoexcept. In contrast,unique_ptr::unique_ptr(nullptr_t) isnoexcept, as per 20.3.1.3[unique.ptr.single]:

constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }

Both libstdc++ and libc++ have addednoexcept toshared_ptr::shared_ptr(nullptr_t). Microsoft's STL has not.

[2014-03-26 Library reflector vote]

The issue has been identified as Tentatively Ready based on six votes in favour.

Proposed resolution:

This wording is relative to N3936.

1. Change class templateshared_ptr synopsis, 20.3.2.2[util.smartptr.shared], as indicated:

   constexpr shared_ptr(nullptr_t)noexcept : shared_ptr() { }