3068. Forbid assigning an rvalue basic_string to basic_string_view

Section: 27.3.3 [string.view.template] Status: NAD Submitter: Antony Polukhin Opened: 2018-02-19 Last modified: 2022-08-24

Priority: 2

View all other issues in [string.view.template].

View all issues with NAD status.

Discussion:

It is known that we cannot disable move construction of basic_string_view from rvalues of basic_string, because it breaks a valid use case:

string foo();
void bar(string_view );
bar(foo());

Though it is still possible to disable an absolutely wrong case of assigning an rvalue basic_string to basic_string_view:

string_view sw = "Hello";
sw = foo();

Some tests that make sure that other use cases are not affected are available here

[2018-06-18 after reflector discussion]

Priority set to 2; status to LEWG

[2020-05-28; LEWG issue reviewing]

LEWG issue processing voted to reject 3068 as NAD. Status change to Open.

SF F N A SA
15 5 1 0 0

[2022-08-24 Status changed: Open → NAD.]

LWG telecon: close based on LEWG direction. "This makes string_view depend on basic_string." "Request a paper with implementation if someone really wants this."

Proposed resolution:

This wording is relative to N4727.

1. Change 27.3.3 [string.view.template], class template basic_string_view synopsis, as indicated:

   […]
   // 27.3.3.2 [string.view.cons], construction and assignment
   constexpr basic_string_view() noexcept;
   constexpr basic_string_view(const basic_string_view&) noexcept = default;
   constexpr basic_string_view& operator=(const basic_string_view&) noexcept = default;
   template <class A>
   basic_string_view& operator=(const basic_string<charT, traits, A>&&) = delete;
   constexpr basic_string_view(const charT* str);
   constexpr basic_string_view(const charT* str, size_type len);
   […]