Changed in v3: added include of <type_traits> v2: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604137.html v1: https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598189.html
On Tue, 2022-07-12 at 07:48 +0100, Jonathan Wakely wrote: > 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 [...snip...] > > +#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. I've added an include of <type_traits> in this version of the patch. > > > + > > +/* 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 > > > > This patch adds gcc/make-unique.h, containing a minimal C++11 implementation of make_unique (std::make_unique is C++14). Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu in conjunction with a followup series of patches which use this in dozens of places in the analyzer. OK for trunk? gcc/ChangeLog: * make-unique.h: New file. --- gcc/make-unique.h | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 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..c9a7d6ef6ce --- /dev/null +++ b/gcc/make-unique.h @@ -0,0 +1,44 @@ +/* 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 <memory> must be included + from system.h by defining INCLUDE_MEMORY in any source file using + make-unique.h. */ + +#ifndef INCLUDE_MEMORY +# error "You must define INCLUDE_MEMORY before including system.h to use make-unique.h" +#endif + +#include <type_traits> + +/* 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
