On Mon, 22 Mar 2021 at 13:31, David Blaikie <dblai...@gmail.com> wrote:
> On Thu, Mar 18, 2021 at 7:58 PM Richard Smith via cfe-commits < > cfe-commits@lists.llvm.org> wrote: > >> >> Author: Richard Smith >> Date: 2021-03-18T19:58:21-07:00 >> New Revision: 5c689e4bb0473e08645547ddbf9874b5e2fa04d0 >> >> URL: >> https://github.com/llvm/llvm-project/commit/5c689e4bb0473e08645547ddbf9874b5e2fa04d0 >> DIFF: >> https://github.com/llvm/llvm-project/commit/5c689e4bb0473e08645547ddbf9874b5e2fa04d0.diff >> >> LOG: Improve documentation for the [[clang::lifetimebound]] attribute. >> >> Added: >> >> >> Modified: >> clang/include/clang/Basic/AttrDocs.td >> >> Removed: >> >> >> >> >> ################################################################################ >> diff --git a/clang/include/clang/Basic/AttrDocs.td >> b/clang/include/clang/Basic/AttrDocs.td >> index f73fbd08e3bf..734cf026ae87 100644 >> --- a/clang/include/clang/Basic/AttrDocs.td >> +++ b/clang/include/clang/Basic/AttrDocs.td >> @@ -3032,10 +3032,39 @@ is retained by the return value of the annotated >> function >> (or, for a parameter of a constructor, in the value of the constructed >> object). >> It is only supported in C++. >> >> -This attribute provides an experimental implementation of the facility >> -described in the C++ committee paper `P0936R0 <http://wg21.link/p0936r0 >> >`_, >> -and is subject to change as the design of the corresponding functionality >> -changes. >> +This attribute causes warnings to be produced if a temporary object does >> not >> +live long enough. For example: >> + >> +.. code-block:: c++ >> + >> + template<typename T, typename U> >> + const U &get_or_default(std::map<T, U> &m, const T &key, >> + const U &default_value >> [[clang::lifetimebound]]); >> + >> + std::map<std::string, std::string> m; >> + // warning: temporary "bar"s that might be bound to local reference >> 'val' >> + // will be destroyed at the end of the full-expression >> + const std::string &val = get_or_default(m, "foo"s, "bar"s); >> + >> +When applied to a reference parameter, the referenced object is assumed >> to be >> +retained by the return value of the function. When applied to a >> non-reference >> +parameter (for example, a pointer or a class type), all temporaries >> referenced >> +by the parameter are assumed to be retained by the return value of the >> +function. >> > > "referenced by" seems a bit vague to me - I guess it means all reference > members of the parameter? (what about reference members of subobjects?) > I'll send you a further improvement to review :) > + >> +The attribute can be applied to the implicit ``this`` parameter of a >> member >> +function by writing the attribute after the function type: >> + >> +.. code-block:: c++ >> + >> + struct string_view { >> + // ... >> + const char *data() const [[clang::lifetimebound]]; >> + }; >> + >> +This attribute is inspired by the C++ committee paper `P0936R0 >> +<http://wg21.link/p0936r0>`_, but does not affect whether temporary >> objects >> +have their lifetimes extended. >> }]; >> } >> >> >> >> >> _______________________________________________ >> cfe-commits mailing list >> cfe-commits@lists.llvm.org >> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >> >
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