On Tue, 12 Jul 2022, 01:25 David Malcolm, <dmalc...@redhat.com> wrote:
> On Fri, 2022-07-08 at 22:16 +0100, Jonathan Wakely wrote: > > On Fri, 8 Jul 2022 at 21:47, David Malcolm via Gcc <g...@gcc.gnu.org> > > wrote: > > > > > > std::unique_ptr is C++11, and I'd like to use it in the > > > gcc/analyzer > > > subdirectory, at least. The following patch eliminates a bunch of > > > "takes ownership" comments and manual "delete" invocations in favor > > > of simply using std::unique_ptr. > > > > > > The problem is that the patch makes use of std::make_unique, but > > > that > > > was added in C++14. > > > > > > I've heard that it's reasonably easy to reimplement > > > std::make_unique, > > > but I'm not sure that my C++11 skills are up to it. > > > > You know we have an implementation of std::make_unique in GCC, with a > > GCC-compatible licence that you can look at, right? :-) > > > > But it's not really necessary. There are only two reasons to prefer > > make_unique over just allocating an object with new and constructing > > a > > unique_ptr from it: > > > > 1) avoid a "naked" new in your code (some coding styles like this, > > but > > it's not really important as long as the 'delete' is managed > > automatically by unique_ptr). > > > > 2) exception-safety when allocating multiple objects as args to a > > function, see https://herbsutter.com/gotw/_102/ for details. > > Irrelevant for GCC, because we build without exceptions. > > [moving from gcc to gcc-patches mailing list] > > Also, I *think* it's a lot less typing, since I can write just: > > std::make_unique<name_of_type_which_could_be_long> (args) > > rather than > > std::unique_ptr<name_of_type_which_could_be_long> (new > name_of_type_which_could_be_long (args)); > > > > > > > > > > Is there: > > > (a) an easy way to implement a std::make_unique replacement > > > (e.g. in system.h? what to call it?), or > > > > If you don't care about using it to create unique_ptr<T[]> arrays, > > it's trivial: > > > > template<typename T, typename... Args> > > inline typename std::enable_if<!std::is_array<T>::value, > > std::unique_ptr<T>>::type > > make_unique(Args&&... args) > > { return std::unique_ptr<T>(new T(std::forward<Args>(args)...)); > > } > > > > To add the overload that works for arrays is a little trickier. > > Thanks! > > I tried adding it to gcc/system.h, but anything that uses it needs to > have std::unique_ptr declared, which meant forcibly including <memory> > from gcc/system.h > > So instead, here's a patch that adds a new gcc/make-unique.h header, > containing just the template decl above (in the root namespace, rather > than std::, which saves a bit more typing). > Adding things to std isn't allowed anyway, so that's correct. > I've successfully bootstrapped®ression-tested a version of my earlier > analyzer patch that uses this patch (see patch 2 of the kit, which has > lots of usage examples). > > OK for trunk? > > Dave > > > > This patch adds gcc/make-unique.h, containing a minimal C++11 > implementation of make_unique (std::make_unique is C++14). > > gcc/ChangeLog: > * make-unique.h: New file. > > Signed-off-by: David Malcolm <dmalc...@redhat.com> > --- > gcc/make-unique.h | 41 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 41 insertions(+) > create mode 100644 gcc/make-unique.h > > diff --git a/gcc/make-unique.h b/gcc/make-unique.h > new file mode 100644 > index 00000000000..c99c5328545 > --- /dev/null > +++ b/gcc/make-unique.h > @@ -0,0 +1,41 @@ > +/* Minimal implementation of make_unique for C++11 compatibility. > + Copyright (C) 2022 Free Software Foundation, Inc. > + > +This file is part of GCC. > + > +GCC is free software; you can redistribute it and/or modify it under > +the terms of the GNU General Public License as published by the Free > +Software Foundation; either version 3, or (at your option) any later > +version. > + > +GCC is distributed in the hope that it will be useful, but WITHOUT ANY > +WARRANTY; without even the implied warranty of MERCHANTABILITY or > +FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License > +for more details. > + > +You should have received a copy of the GNU General Public License > +along with GCC; see the file COPYING3. If not see > +<http://www.gnu.org/licenses/>. */ > + > +#ifndef GCC_MAKE_UNIQUE > +#define GCC_MAKE_UNIQUE > + > +/* This header uses std::unique_ptr, but <memory> can't be directly > + included due to issues with macros. Hence it must be included from > + system.h by defining INCLUDE_MEMORY in any source file using it. */ > + > +#ifndef INCLUDE_MEMORY > +# error "You must define INCLUDE_MEMORY before including system.h to use > make-unique.h" > +#endif > You also need <type_traits> for the enable_if and is_array traits. With libstdc++ that gets included by <memory> but that's guaranteed for other library implementations. I don't know if that had the same kind of issues as other system headers or if it can just be included here. + > +/* Minimal implementation of make_unique for C++11 compatibility > + (std::make_unique is C++14). */ > + > +template<typename T, typename... Args> > +inline typename std::enable_if<!std::is_array<T>::value, > std::unique_ptr<T>>::type > +make_unique(Args&&... args) > +{ > + return std::unique_ptr<T> (new T (std::forward<Args> (args)...)); > +} > + > +#endif /* ! GCC_MAKE_UNIQUE */ > -- > 2.26.3 > >
