From 21ad1b2419ec988d286d15206c133f729c0a313e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20Kr=C3=BCgler?= Date: Sat, 14 Oct 2023 15:40:27 +0200 Subject: [PATCH] =?UTF-8?q?New=20issue=20from=20Peter=20Sommerlad:=20"basi?= =?UTF-8?q?c=5Fstringbuf::str()&&=20should=20enforce=20=F0=9D=92=AA(1)"?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- xml/issue3992.xml | 69 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 69 insertions(+) create mode 100644 xml/issue3992.xml diff --git a/xml/issue3992.xml b/xml/issue3992.xml new file mode 100644 index 0000000000..6aadead913 --- /dev/null +++ b/xml/issue3992.xml @@ -0,0 +1,69 @@ + + + + +<tt>basic_stringbuf::str()&&</tt> should enforce 𝒪(1) +
+Peter Sommerlad +05 Oct 2023 +99 + + +

+Recent discussions on llvm-64644 +came to the conclusion that basic_stringbuf() && introduced by +might just copy the underlying buffer into a string object and not actually move the allocated space. +While the wording tried to encourage that, especially with the postcondition that the buffer must +be empty afterwards, it failed to specify that the move is never a copy. +

+I suggest to amend the specification to enforce implementors to do the 𝒪(1) thing. +There might be ABI issues for those who still copy. +

+Some investigation into p.16 and +shows that a basic_string as a standard container should move with 𝒪(1). +

+Unfortunately, we cannot say +

+

+str().data() == buf.data() before calling str() +

+

+as a postcondition due to SSO. Maybe a note could be added to eliminate the confusion. +

+ + + +

+This wording is relative to . +

+ +
    + +

  1. Modify as indicated:

    + +
    +
    +basic_string<charT, traits, Allocator> str() &&;
+
    +
    +

    +-9- Postconditions: The underlying character sequence buf is empty and pbase(), pptr(), +epptr(), eback(), gptr(), and egptr() are initialized as if by calling +init_buf_ptrs() with an empty buf. +

    +-10- Returns: A basic_string<charT, traits, Allocator> object move constructed from the +basic_stringbuf's underlying character sequence in buf. This can be achieved by first adjusting buf +to have the same content as view(). +

    +[Note: — require the move construction of the return +value to be 𝒪(1) end note] +

    +
    +
    + +
    2. + +
+ + +