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### 3068. Forbid assigning an rvalue `basic_string` to `basic_string_view`

Section: 23.3.3 [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 23.3.3 [string.view.template], class template `basic_string_view` synopsis, as indicated:

   >     […]
   >     // 23.3.3.2 [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);
   >     […]