From: Jonathan Wakely <jwakely@redhat.com>
To: "Daniel Krügler" <daniel.kruegler@gmail.com>
Cc: libstdc++ <libstdc++@gcc.gnu.org>,
gcc-patches List <gcc-patches@gcc.gnu.org>
Subject: Re: [patch] Implement ISO/IEC TS 18822 C++ File system TS
Date: Fri, 01 May 2015 18:22:00 -0000 [thread overview]
Message-ID: <20150501182223.GI3618@redhat.com> (raw)
In-Reply-To: <CAGNvRgAzHFMbsw3PLzEb4zprmGnZiLJux+vJCxY9kC-gCOhvLg@mail.gmail.com>
On 01/05/15 19:03 +0200, Daniel Krügler wrote:
>b/libstdc++-v3/src/filesystem/path.cc:
>
>- path::compare(const path& p) const noexcept:
>
>Shouldn't the implementation of this noexcept function not try to
>create copies of path objects? Couldn't _Cmpt just hold references to
>_M_pathname?
All your other comments are definitely correct and I'll make the
relevant fixes soon, but I'm not sure what you mean here, could you
clarify?
I think it would be possible to implement a path like:
class path
{
using value_type = ...;
using string_type = basic_string<value_type>;
struct _Cmpt;
using composite_path = pair<string_type, list<_Cmpt>>;
using sub_path = basic_string_view<value_type>;
variant<composite_path, sub_path> _M_data;
enum _Type { ... } _M_type;
};
struct _Cmpt : path
{
// ...
};
With the invariant that for all objects of type _Cmpt the variant
member holds a string_view that refers to the string_type object in
some other path.
This would reduce the memory footprint of a path object (but for the
new std::string ABI, only if there are path components longer than the
SSO small string buffer). Even with that design, paths would still
be sizeof(string_type) + sizeof(std::list<_Cmpt>) + sizeof(_Type).
Alternatively, it could be done without a variant, just adding a
string_view member to the path type, which would make it even larger,
but would simplify the implementation.
next prev parent reply other threads:[~2015-05-01 18:22 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-30 17:42 Jonathan Wakely
2015-04-30 19:33 ` Jonathan Wakely
[not found] ` <CAFW6PZB9WvskzrKCsNKK4s-5oXWjcwkuZGMrWbrfgJ7fpJiCXQ@mail.gmail.com>
[not found] ` <20150501105351.GY3618@redhat.com>
2015-05-01 19:49 ` Jonathan Wakely
2015-05-02 9:52 ` Jonathan Wakely
2015-05-08 11:43 ` Rainer Orth
2015-05-13 10:56 ` Jonathan Wakely
2015-05-01 12:45 ` Rainer Orth
2015-05-01 15:11 ` Jonathan Wakely
2015-05-01 15:14 ` Rainer Orth
2015-05-01 17:03 ` Daniel Krügler
2015-05-01 17:55 ` Jonathan Wakely
2015-05-01 18:22 ` Jonathan Wakely [this message]
2015-05-01 19:28 ` Daniel Krügler
2015-05-01 19:38 ` Jonathan Wakely
2015-05-01 20:05 ` Jonathan Wakely
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